WO2023046307A1 - [6r]-mthf in 5-fu based chemotherapy of right-sided colorectal cancer - Google Patents

Abstract

The present invention relates to the treatment of right-sided colorectal cancer in human populations having a high frequency of poor prognostic factors, including BRAF- and KRAS mutations, which involves administering multiple boluses of [6R]-5,10-methylenetetrahydrofolate ([6R]-MTHF) in connection with 5-fluorouracil (5-FU) based chemotherapy.

Description

[6R]-MTHF IN 5-FU BASED CHEMOTHERAPY OF RIGHT-SIDED COLORECTAL CANCER

BACKGROUND OF THE INVENTION

Colorectal cancer (CRC) is one of the leading causes of mortality and morbidity in the world. With approximately 1,849,518 new cases estimated and 880,792 deaths per year (Caputo 2019), it also represents the third most common cancer worldwide and the second cause of cancer-related mortality, after lung cancer. In terms of geographical distribution, CRC incidence and prevalence have risen in industrialized countries (Bray 2018). Colorectal cancer affects approximately 135.439 estimated new patients in the United States per year. Of these cases, 39.910 per year (30%) are due to rectal cancer (Recio-Boiles 2020). However, in recent years the incidence and mortality rates of CRC have grown higher in Eastern Europe, Latin America, and Asia than other countries.

While the 5-year survival rate is 90% for early-stage CRC patients with localized disease, it is 70% for intermediate (regional invasive tumors) and 10% for advanced-stage patients with distant metastasis. Several factors including age, diet, hereditary polyposis syndrome and inflam- matory bowel disease are associated with the development of CRC (Brenner 2014). However, CRC is not a single type of tumor; its pathogenesis depends on the anatomical location of the tumor and differs between right side and left side of the colon. Right-sided CRC (RCRC) tumors arise from the ascending colon, and proximal two thirds of the transverse colon whereas the left-sided CRC (LCRC) tumors arise from the descending and sigmoid colon, and distal one third of the transverse colon.

The importance of CRC sidedness in terms of treatment outcome was first addressed by Dr Alan Venook who presented his analysis in 2016 (Venook 2016). For patients with metastatic colorectal cancer, he found, the sidedness of the primary tumor within the colon appears to affect both survival and the effectiveness of the commonly used biological agents Avastin (bevacizumab) and Erbitux (cetuximab), which are designed to interfere with the formation of blood vessels that feed a tumor, and with growth factor receptor signaling. Patients with left-sided disease enjoyed a median overall survival of 33 months compared with 19.4 months in right-sided disease. A fur- ther comparison of Avastin and Erbitux showed that Erbitux might be harmful to patients with right-sided tumors.

Tumors in the proximal colon (right side, RCRC) and distal colon (left side, LCRC) exhibit different molecular characteristics and histology. In fact, the two sides of the colon emerge from different parts of embryo. Some cells become the right colon, while others become the left colon. The right colon comes from the mid gut while the left colon comes from the hind gut, and they have different blood supplies. The cells on the left and right sides function slightly differently, and therefore, while they possess the same genes, they may not all be turned on to express the same set of proteins. Further, the right colon has a different embryological origin and blood supply from the left colon and rectum. The superior mesenteric artery thus supplies midgut structures from the mid-duodenum to the mid-transverse colon, whereas the inferior mesenteric artery supplies hindgut structures from the mid-transverse colon to the rectum.

In the RCRC tumors, mutations in the DNA mismatch repair pathway are commonly observed; and these tumors generally have a flat histology. In the LCRC tumors, chromosomal instability pathway-related mutations, such as KRAS, APC, PIK3CA, p53 mutations are observed and these tumors demonstrate polypoid-like morphology. Therapy responses are totally different between these tumor entities. LCRC patients benefit more from adjuvant chemotherapies such as 5-fluorouracil (5-FU)-based regimes, and targeted therapies such as anti-epidermal growth factor receptor (EGFR) therapy, and have a better prognosis. RCRC patients do not respond well to conventional chemotherapies, but demonstrate more promising results with immunotherapies because these tumors have high antigenic load (Baran 2018).

Metastasis of CRC significantly affects the overall survival among the patients. Distant metastases are present in approximately 25% of patients; diagnosis and resectability of metastasis significantly dictates the outcome. The sites of metastasis differ between LCRC and RCRC patients. While LCRC patients tend to have liver and lung metastasis, RCRC patients have peritoneal carci- nomatosis. Thus, CRC acts as two different diseases in the same organ (Baran 2018, Ross 2018). "Segregating patients according to RCRC v LCRC is a useful and pragmatic approach to guide decision-making regarding biological agents and should be adopted by oncologists in clinical practice" (Ross 2018).

Several publications highlight the differences between gene expressions in right- and left-sided CRCs. One example, which may explain the activity of epidermal growth factor receptor (EGFR) monoclonal antibodies ("mabs"), is that LCRC tumors overexpress genes involved in the EGFR pathway including the ligands for the EGFR receptor, epiregulin and amphiregulin. On the contrary, the higher methylation status of RCRC cancers results in these same genes being silenced (Burge 2019). Thus, anti-EGFR therapy benefits primarily those patients with left-sided or distal tumors (Hanna 2020).

On the basis of their molecular and clinical differences, left-sided and right-sided colorectal tumors are thus now recognized as unigue cancers, that respond to different therapeutic strategies (Hanna 2020). See also Burge 2020 and Figure 1 herein.

Separately from the issue of sidedness, mCRC can also be classified into different subtypes characterized by specific molecular and morphological variations. BRAF is a protein in the EGFR- mediated MAPK pathway; its downstream signalling activates MEK through its phosphorylation. BRAF mutations are found in 8-12% of cases of mCRC, with the predominance of BRAF^V600E in approximately 90% of BRAF-mutant CRC. BRAF^V600E is a point mutation at nucleotide 1799 that results in independent activation of its upstream activator protein, RAS, as well as increased stimulation of its downstream effector proteins, MEK and ERK, via phosphorylation. RAS and BRAF mutations are usually mutually exclusive (Tabernero 2020).

Several studies have demonstrated a significant difference in prognostic outcome between patients with right- and left-sided colon cancers. One such study by Peng et al. analyzed a group of patients who had undergone curative resection and oxaliplatin-based adjuvant chemotherapy. Patients with RCRC exhibited a worse 3-year OS than those with LCRC (Peng 2018). Previous studies also reported that patients with stage III RCRC often present a significantly increased mortality risk compared with those with LCRC. (Sinicrope 2013). This can be explained by the fact that RCRC tends to be associated with BRAF mutations (Sideris 2015) which have been found to occur in ~33% of all patients with right-sided CRC (Taniguchi 2020). In particular, the BRAF^V600E mutation, also observed in melanoma, is associated with a very poor prognosis and a median survival of less than 12 months.

In terms of treatment, RCRC patients with BRAF-mutations do not benefit from therapeutics targeting the epidermal growth factor receptor (EGFR). Folate/5-FU assisted oxaliplatin-based chemotherapy plus bevacizumab is the current standard therapy in first-line treatment of BRAF-mutated RCRC, including the more intensive "triplet" therapy FOLFOXIRI (i.e. leucovorin/5-FU/oxaliplatin/ irinotecan) plus bevacizumab, which however is only a valid option in patients with a good ECOG (Eastern Cooperative Oncology Group) performance status (Caputo 2019). Triplet chemotherapy has thus been found to be a very good option for fit RCRC patients with aggressive tumors.

However, FOLFOXIRI plus bevacizumab triplet therapy is in general associated with an highly increased level of adverse effects. In a meta-analysis of patient data from 5 clinical studies it was thus found that - compared with patients receiving doublet therapy (FOLFOX or FOLFIRI) - patients in the triplet group (FOLFOXIRI plus bevacizumab) had higher rates of grade 3 or 4 neutropenia (45.8% vs 21.5%, P < .001), febrile neutropenia (6.3% vs 3.7%, P = .019), nausea (5.5% vs 3.0%, P = .016), mucositis (5.1% vs 2.9%, P = .024), and diarrhea (17.8% vs 8.4%, P < .001). Death due to toxicity occurred in 2.3% vs 1.4% of patients (P = .277) (Cremolini 2020).

FOLFOXIRI plus bevacizumab triplet therapy therefore remains recommended only to patients whose general condition is very good, estimated to around 40-50% of all mCRC patients; discounting the elderly (Cremolini 2019).

Sadly, it is not the majority of mCRC patients who are sufficiently fit, young enough or have an ECOG status of 0, to be subjected to FOLFOXIRI plus bevacizumab triplet therapy. For the majority of patients with right-sided mCRC, including patients determined by genotype testing to be BRAF mutation-positive, there remains an unmet need for an improved folate-enhanced 5-FU treatment protocol of their disease.

DEFINITIONS

As used herein, the term Leucovorin® or folinic acid shall both mean 5-formyl tetrahydrofolic acid, i.e. the 5-formyl derivative of tetrahydrofolic acid. Folinic acid contains 2 asymmetric centers. Commercially available leucovorin (LV) is composed of a 1:1 mixture of the dextrorotary and levo- rotary diastereomers (d-leucovorin (d-LV, (6R,2'S)-configuration) and /-leucovorin (/-LV, (6S,2'S)- configuration), respectively), and may also be referred to as (d,/-LV).

As used herein, the term levoleucovorin shall refer to the commercially available product which contains only the pharmacologically active levo-isomer /-LV (or LLV). In vitro, /-LV has been shown to be rapidly converted to the biologically available methyl-tetrahydrofolate form while the dextro form d-LV (DLV) is slowly excreted by the kidneys. Leucovorin and levoleucovorin have however been shown to be pharmacokinetically identical with respect to the content of levoleucovorin, and may be used interchangeably with limited differences in efficacy or side effects (Kovoor et al, Clin Colorectal Cancer 8 200-6 (2009).

As used herein, the terms MTHF or methyleneTHF shall both refer to 5,10-Methylene-5,6,7,8- tetrahydrofolate.

As used herein, the terms racemic methyleneTHF, CoFactor® or [6R,S]-5,10-methyleneTHF shall all refer to the 1:1 diastereomeric mixture [6R,S]-5,10-Methylene-5,6,7,8-tetrahydrofolate.

As used herein, the terms [6R]-5,10-MTHF and [6R]-MTHF s all both refer to the single diastereomer, [6R]-5,10-methylenetetrahydrofolate. As used herein, the terms IV or i.v. shall both mean intravenous.

As used herein, the term DLT shall refer to dose-limiting toxicity. Dose Limiting Toxicity (DLT) is a medical occurrence that is assessed as at least possibly related to a pharmaceutical product (i.e. to one or more chemotherapeutic agents) and is severe enough to prevent further increase in dosage or strength of treatment agent, or to prevent continuation of treatment at any dosage level.

As used herein, the term ORR shall refer to the Objective Response Rate, ie. the proportion of patients with reduction in tumor burden of a predefined amount. This shall be calculated as fol- lows: ORR = Sum of partial responses plus complete responses as per RECIST 1.1 (a set of published rules that define when tumors in cancer patients progress during treatments, the responses being defined as:

Complete Response (CR):

• Disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm.

Partial Response (PR):

• At least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters.

Progressive Disease (PD):

• At least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this includes the baseline sum if that is the smallest on study).

• In addition to the relative increase of 20%, the sum must also demonstrate an abso- lute increase of at least 5 mm. (Note: the appearance of one or more new lesions is also considered progression).

Stable Disease (SD):

• Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study.

(Eisenhauer EA, Therasse P, Bogaerts J, Schwartz LH, Sargent D, Ford R, et al. New response evaluation criteria in solid tumors: revised RECIST guideline (version 1.1). Eur J Cancer. 2009 Jan; 45(2):228-47)

As used herein, the term DCR shall refer to the Disease Control Rate, i.e. the proportion of patients with either Stable Disease or Partial Response, as defined hereinabove.

As used herein, the term dU shall refer to deoxyuridine. As used herein, the term BSA refers to Body Surface Area

As used herein, the terms BRAF mutation-positive patients and KRAS mutation-positive patients shall refer to patients who by genotype testing have been found to harbor either BRAF- or KRAS mutated tumors and/or metastases.

As used herein, the term ctDNA genotype testing shall refer to genotype testing conducted by analyzing a blood or serum sample for cell-free tumor DNA.

As used herein, the term right-sided colorectal cancer shall refer to patient cases wherein the primary tumor of said patient has been determined to be located in the cecum, ascending colon, hepatic flexure and/or transverse colon.

SUMMARY OF INVENTION

Arfolitixorin (Modufolin®) is a new drug developed to increase the efficacy of the cytotoxic agent 5-fluorouracil (5-FU) and as a rescue drug after high-dose methotrexate treatment. Arfolitixorin (Modufolin®), [6R]-5,10-methylenetetrahydrofolate, abbreviated herein as [6R]-5,10-MTHF, needs to be metabolically formed when using the widely used folate-based drugs leucovorin and levoleucovorin. Arfolitixorin (Modufolin®), however, does not require metabolic activation to exert its effect and may therefore be suitable for all patients.

According to the present invention, it has surprisingly been found that patients diagnosed with right-sided colorectal cancer, including patients determined by genotype testing to be either BRAF mutation-positive or KRAS mutation-positive or both BRAF mutation-positive and KRAS mu- tation-positive, i.e. harboring BRAF mutation- and/or KRAS mutation-positive colorectal cancer tumors, may be treated according to a chemotherapeutic protocol over at least 16 weeks involving i.a. administration of multiple, rapid boluses of [6R]-5,10-MTHF, by which treatment best ORRs (objective response rates) of >50% can be achieved.

Accordingly, in a first aspect of the invention, [6R]-5,10-methylenetetrahydrofolate ( [6R]- 5,10-MTHF) is provided for use in a human in the treatment of solid colorectal cancer tumors, which treatment comprises the following steps: a) administering a continuous IV infusion containing 85 mg/m² (of BSA) oxaliplatin, fol- lowed by b) administering an IV bolus containing 400 mg/m² (of BSA) 5-fluorouracil, followed by c) administering an IV bolus containing 60 mg/m² [6R]-5,10-methylenetetrahydrofolate, followed by d) administering a continuous IV infusion containing 2400 mg/m² 5-fluorouracil over 46 hours ± 1 hour followed by e) administering an IV bolus containing 60 mg/m² (of BSA) [6R]-5,10-methylenetetrahy- drofolate, wherein the location of the primary tumor of said patient has been determined to be right-sided, and wherein all steps a) - e) are repeated every 2 weeks until termination of the treatment, and wherein all steps a) - e) are repeated every 2 weeks for at least 16 weeks, until termination of the treatment.

In a second aspect of the invention, [6R]-5,10-methylenetetrahydrofolate ([6R]-5,10-MTHF) is pro- vided for use in a human in the treatment of solid colorectal cancer tumors, which treatment comprises the following steps a) administering a continuous IV infusion containing 180 mg/m² (of BSA) irinotecan, fol- lowed by b) administering an IV bolus containing 400 mg/m² (of BSA) 5-fluorouracil, f by c) administering an IV bolus containing 60 mg/m² [6R]-5,10-methylenetetrahydrofolate, fol- lowed by d) administering a continuous IV infusion containing 2400 mg/m² 5-fluorouracil over 46 hours ± 1 hour followed by e) administering an IV bolus containing 60 mg/m² (of BSA) [6R]-5,10-methylenetetrahydro- folate, wherein the location of the primary tumor of said patient has been determined to be right-sided, and wherein all steps a) - e) are repeated every 2 weeks until termination of the treatment, and wherein all steps a) - e) are repeated every 2 weeks for at least 16 weeks, until termination of the treatment.

The treatment based on the ARFOX or ARFIRI protocol may in principle be terminated "for any reason", such as e.g. by a patient decision or a decision taken by the responsible medical person, i.a. due to disease progression or adverse events. Furthermore, the ARFOX or ARFIRI protocol may be interrupted by treatment holidays and the like. Finally the responsible medical person may decide on a fixed number of treatment cycles. It has also surprisingly been discovered that administration of [6R]-MTHF and 5-FU according to the first or second aspect of the present invention over a treatment period of at least 16 weeks leads to a retardation or prevention of the progression of solid colorectal cancer tumors in a human patient diagnosed with right-sided colorectal cancer, including patients determined by genotype testing to be either KRAS or BRAF mutation-positive.

In a third aspect of the invention [6R]-5,10-methylene-tetrahydrofolate is therefore provided for use in the retardation or prevention of the progression of solid colorectal cancer tumors in a human patient diagnosed with right-sided colorectal cancer, wherein said human patient has been found by genotype testing to be either BRAF mutation-positive or KRAS mutation-positive or both BRAF mutation-positive and KRAS mutation-positive, which comprises performing and repeating steps a) to e) according to the first or second aspect of the present invention, over a total treatment period of at least 16 weeks.

In a fourth aspect of the invention, there is provided a method for retardation or prevention of the progression of solid colorectal cancer tumors in a human diagnosed with right-sided colorectal cancer, wherein said human patient has been found by genotype testing to be either BRAF muta- tion-positive or KRAS mutation-positive or both BRAF mutation-positive and KRAS mutation-posi- tive, which method comprises performing and repeating steps a) to e) according to the first or second aspect of the present invention, over a total treatment period of at least 16 weeks.

DESCRIPTION OF FIGURES

Figure 1 (adapted from Burge 2019): An overview of some differences between left- and right sided CRC.

Figure 2 is a table of all the 31 participating patients in the follow-up study including a status for each patient as regards KRAS and BRAF genotype results. DETAILED DESCRIPTION OF THE INVENTION

Arfolitixorin has been in development for a number of years and has been studied in several clinical studies. During one of these studies (the Phase l/lla study ISO-CC-005) it was surprisingly discovered in December 2017 that administration of [6R]-MTHF and 5-FU according to a particular treatment regimen over a treatment period of at least 8 weeks lead to a prevention or retarding of the progression in a human of solid tumors. No statistically significant progression of said solid tumors was observed between 8 and 16 weeks after initiating treatment. These results are discussed i.a. in applicant's international patent application WO 2019/037899 published 28 February 2019. The completion of the study was announced in January 2020. In total, 105 patients were included in the study.

Applicant completed the dose definition part of ISO-CC-005 in March 2018, which evaluated the safety and efficacy of arfolitixorin in patients with mCRC. Shortly after, applicant started two additional treatment groups in 2018 to generate more safety and efficacy data, i.e. the safety extension Cohort #18 (Treatment Arm #4) and Cohort #19 (Treatment Arm #6). The aim was to evaluate as many patients as possible from the additional treatment groups after a treatment period of 16 weeks+.

On 30 September 2020, applicant announced response assessment data from the two safety extension cohorts (31 patients) treated for 16 weeks or longer (press release: 55 % Overall Response Rate on the safety extension cohorts of the ISO-CC-005 Phase l/lla study | BioSpace). The data showed a best overall response rate (ORR) of 55 %. These patients had been treated with the selected dose regimen of 120 mg/m² arfolitixorin and 5-fluorouracil (5-FU) with either irinotecan or oxaliplatin (ARFIRI/ARFOX). Out of the 31 patients, 17 were treated with an ARFOX regimen.

A best ORR of 59% was observed in the ARFOX regimen group versus 50% in the ARFIRI regimen group, despite that 53% of the patients had a right-sided tumor location and 24% were carrying a BRAF mutation. As mentioned above, in the general CRC population and in historical control first line mCRC Phase III trials, a percentage of approximately 30-40% right-sided tumors are seen and around 10% of the patients carry a BRAF mutation. Both right-sided tumor location and BRAF mutations are historically known as poor prognostic factors and the best ORR in these patient populations in the first line mCRC setting treated with either FOLFOX or FOLFIRI historically generates best ORRs in the range of ~40% and 15-20% respectively (see eg Loupakis 2018, Van Cutsem 2015 and Tveit 2012). The average ORR based on pivotal Phase III trials considered in a recent meta-analy- sis/review indicates that FOLFOX regimens generates 45% best ORR and FOLFIRI regimens generates 40% best ORR in historical non-selected patient population (all-comer), first line mCRC populations (Giuliani 2018).

During a subsequent assessment of the follow-up study results, applicant has now discovered that some of the tested combinations have proven surprisingly effective against right- sided and BRAF-mutated mCRC tumors. As mentioned hereinabove, these tumor types are particularly aggressive and difficult to treat with cytostatic drugs, and both tumor types are deemed "poor prognostic factors".

The baseline CRC genotype and sidedness status for the patients enrolled in the follow-up study was collected and summarized as follows:

Of the 43 patients enrolled in the two safety extension cohorts, 12 patients were either not evaluated with a CT-scan at 8 weeks or beyond 8 weeks of treatment. Of these 12 patients, 4 patients had Stable Disease (SD) and 3 patients had Partial Response (PR) already after 8 weeks.

Of the 31 patients actually evaluated at 16 weeks (or more), 13 (42%) had right-sided, 13 (42%) had left-sided, 5 (16%) had rectal CRC, 8 (26%) BRAF-mutated CRC and 11 (35%) KRAS- mutated CRC, which corresponds roughly to the composition of the initial group of 43 patients enrolled in the two safety extension cohorts. In total, 19 patients (61%) had either BRAF-mutated CRC or /KRAS-mutated CRC.

The objective response rates (ORRs) for left- and right-sided CRC and rectal cancer have historically been found to be quite different. Patients with LCRC, regardless of the type of treatment received, have superior ORRs compared to patients with RCRC (app. 57% vs 40%, see eg. Grassadonia 2019). This has been corroborated by Sagawa et al. who investigated the prognostic and predictive efficacy of primary tumour location and the impact of early tumour shrinkage (ETS) and depth of response (DpR) on therapeutic outcomes in a cohort of patients with mCRC treated with first-line chemotherapy plus bevacizumab or cetuximab in a Japanese population. It was thus confirmed that left-sided tumours showed signifcantly higher ORR than the right-sided tumours (67.1% vs 44.1%; p=0.003, Sagawa 2020). Based on ORRs alone, the treatment of right-sided col- orectal cancer patients must therefore be seen as a different, more challenging task than the treatment of colorectal cancer patients in general. As mentioned in the background section of the present application, there are moreover many other reasons for considering left- and right-sided CRC tumors separate cases.

Further, apart from the question of sidedness the ORRs have also been found to be very different for patients with BRAF wild-type (wt) vs. mutant (mt) tumors. ORRs were thus found to be 15-20% in patients with BRAF (mt) tumors vs. 50% in those with BRAF (wt) tumors (Li 2020). Right-sided CRC patients are often found to be BRAF mutation-positive by genotype testing.

The ORRs have on the other hand in a number of studies been found to be quite similar (around 41%) for patients with KRAS (wt)-type vs. KRAS (mt) CRC. Thus, in a Chinese study comprising 141 patients with known KRAS status, 55 patients harbored KRAS-mutated and 86 wild-type tumors. The group was treated according to different chemotherapeutic regimens, most including bevaci- zumab, and achieved ORR and DCR of 41.9% and 78.9% in patients with KRAS (wt), while the ORR and DCR were 38.7% and 77.9% in patients with KRAS mutation (Sun 2017). This similarity was confirmed in a Greek study with patients in first line chemotherapy with bevacizumab. The ORRs for FOLFOX/BEV was 48.3% (115 pts), FOLFIRI/BEV 47.7% (92pts) and XELOX/BEV 45% (65pts), regardless of KRAS status (Koumarianou 2018).

Several clinical studies have thus found the following approximate ORRs for RCRC patients with or without BRAF- or KRAS-mutations:

• ORR = 40% for RCRC without mutations

• ORR = 20% for CRC with BRAF mutations

• ORR = 40% for CRC with KRAS mutations Returning now to the 31 patients from the follow-up study evaluated at 16 weeks (or more), the "RCRC group" of 13 patients. Upon further analysis this group contained:

• 3 cases of RCRC with BRAF mutations (23%)

• 5 cases of RCRC with KRAS mutations (38%)

• 5 cases of RCRC with either wild type or unknown type (38%)

This 31-patients group would be expected to have an overall best ORR reflecting the proportion of patients with RCRC (no mutations) + the proportion of patients with BRAF(mt) CRC + the proportion of patients with KRAS(mt) CRC which can be calculated as follows: Expected ORR_{RCRC group} = Prop_BRAF(mt) *ORR _BRAF(mt) + Prop_KRAS(mt)*ORR_KRAS(mt)+Prop_RCRC*ORR_RCRC which gives, using the historical ORR's discussed above:

Expected ORR_{RCRC group} = 23%* 20% + 38%*40% + 38%*40% = 35%

However, when assessing the results for the 31-patient group after 16 weeks and beyond of treatment with 120 mg/m² arfolitixorin + 5-FU + irinotecan or oxaliplatin (ARFIRI/ARFOX protocol), it was surprisingly found that patients in the 31-patient group diagnosed with RCRC had a best ORR of 46%.

Thus, the ARFIRI/ARFOX treatment protocols have proven surprisingly effective in the treatment of patients with right-sided CRC, including RCRC patients who by genotype testing have been determined to be BRAF- or KRAS mutation-positive.

Accordingly, in a first aspect of the invention, [6R]-5,10-methylenetetrahydrofolate ( [6R]- 5,10-MTHF) is provided for use in a human in the treatment of solid colorectal cancer tumors, which treatment comprises the following steps: a) administering a continuous IV infusion containing 85 mg/m² (of BSA) oxaliplatin, fol- lowed by b) administering an IV bolus containing 400 mg/m² (of BSA) 5-fluorouracil, followed by c) administering an IV bolus containing 60 mg/m² [6R]-5,10-methylenetetrahydrofolate, followed by d) administering a continuous IV infusion containing 2400 mg/m² 5-fluorouracil over 46 hours ± 1 hour followed by e) administering an IV bolus containing 60 mg/m² (of BSA) [6R]-5,10-methylenetetrahy- drofolate, wherein the location of the primary tumor of said patient has been determined to be right-sided, and wherein all steps a) - e) are repeated every 2 weeks until termination of the treatment, and wherein all steps a) - e) are repeated every 2 weeks for at least 16 weeks, until termination of the treatment.

In a second aspect of the invention, [6R]-5,10-methylenetetrahydrofolate ([6R]-5,10-MTHF) is pro- vided for use in a human in the treatment of solid colorectal cancer tumors, which treatment comprises the following steps a) administering a continuous IV infusion containing 180 mg/m² (of BSA) irinotecan, fol- lowed by b) administering an IV bolus containing 400 mg/m² (of BSA) 5-fluorouracil, followed by c) administering an IV bolus containing 60 mg/m² [6R]-5,10-methylenetetrahydrofolate, fol- lowed by d) administering a continuous IV infusion containing 2400 mg/m² 5-fluorouracil over 46 hours ± 1 hour followed by e) administering an IV bolus containing 60 mg/m² (of BSA) [6R]-5,10-methylenetetrahydro- folate, wherein the location of the primary tumor of said patient has been determined to be right-sided, and wherein all steps a) - e) are repeated every 2 weeks until termination of the treatment, and wherein all steps a) - e) are repeated every 2 weeks for at least 16 weeks, until termination of the treatment.

Throughout the present application the treatment regimen according to the first aspect is referred to as the "ARFOX" protocol, and the treatment regimen according to the second aspect is referred to as the "ARFIRI" protocol.

The treatment based on the ARFOX or ARFIRI protocol may in principle be terminated "for any reason", such as e.g. by a patient decision or a decision taken by the responsible medical person, i.a. due to disease progression or adverse events. Furthermore, the ARFOX or ARFIRI protocol may be interrupted by treatment holidays and the like. Finally the responsible medical person may decide on a fixed number of treatment cycles.

As mentioned above, several of the RCRC patients were also determined to br BRAF- or KRAS-mutation positive. In CRC patients the KRAS and BRAF mutation status is traditionally determined by tumor sample analysis. This requires surgery, and the subsequent analysis (extraction of genomic DNA from the tumor biopsy and analysis for mutations using dPCR) often takes weeks to complete. This creates problems in clinical situations which require urgent treatment based on the mutation status of the patient.

However, several studies the past 5-10 years have demonstrated that genotype testing by analysis of circulating, cell-free tumor DNA (ctDNA) in plasma or serum samples is becoming increasingly accurate and thus important as a non-invasive and fast alternative or supplement to tumor sample analysis. The method is also referred to as "Liquid Biopsy" analysis. Cell-free DNA (cfDNA) is fragmented DNA that is found in the non-cellular blood components. Among tumor patients, ctDNA is 150-200 base pair fragments that are released by tumor cells into the bloodstream and represents a small fraction of the total cfDNA. Importantly, ctDNA retains epigenetic characteristics and carries tumor-specific mutations that can be detected in peripheral blood (Bi 2020). Analysis of ctDNA in plasma is based on sequencing assays, see eg Finkle 2021.

It was thus reported (Mas 2019) that in a study involving four hundred and twenty-five enrolled mCRC patients, the paired tumor tissue and plasma samples of the patients showed an accuracy of 97.3% (95% Cl: 95.2-98.6%) between the BRAFstatus in plasma and tissue for patients with available paired samples (n = 405), and 98.5% (95% Cl: 96.4-99.5%) for those with conclusive ctDNA (n = 323).

The absence of liver metastasis was the main factor associated with inconclusive ctDNA results. In patients with liver metastases, the accuracy was 98.6% (95% Cl, 96.5-99.6%).

Similarly, another study (Bachet 2018) involving 329 patients with detectable ctDNA (at least one mutation or one methylated biomarker) showed an accuracy of 94.8% (95% Cl, 91.9% to 97.0%) between the RAS mutation status in plasma and tissue. The absence of liver metastases also here was the main clinical factor associated with inconclusive ctDNA results. Analysis of ctDNA ("liquid biopsy" analysis ) is thus deemed an important tool for determining the relevant patient group according to the first or second aspect of the present invention.

Accordingly, in embodiments of the invention, [6R]-5,10-methylene-tetrahydrofolate is provided for use in a human patient in the treatment of right-sided, solid colorectal cancer tumors, which treatment comprises steps a) - e) according to the first or second aspect of the invention, wherein the human patient has been found either by traditional tumor tissue analysis or in preferred embodiments by ctDNA ("liquid biopsy") analysis to be either BRAF mutation-positive or KRAS mutation-positive or both BRAF mutation-positive and KRAS mutation-positive.

In specific embodiments bevacizumab is administered to a human patient during the treatment period according to the first or second aspect. In further embodiments, bevacizumab is administered to a human patient at a dose of 5 mg/kg as an IV infusion every two weeks. In still further embodiments, bevacizumab administration is initiated 8 weeks after initiating treatment.

It has also surprisingly been discovered that administration of [6R]-MTHF and 5-FU according to the first or second aspect of the present invention over a treatment period of at least 16 weeks lead to a retardation or prevention of the progression of right-sided, solid colorectal cancer tumors in a human patient.

In a third aspect of the invention [6R]-5,10-methylene-tetrahydrofolate is therefore provided for use in the retardation or prevention of the progression in a human patient of right-sided, solid colorectal cancer tumors, which comprises performing and repeating steps a) to e) according to the first or second aspect of the present invention, over a total treatment period of at least 16 weeks.

In a preferred embodiment of the third aspect, there is provided [6R]-5,10-methylene- tetrahydrofolate for use in the retardation or prevention of the progression of the progression in a human of right-sided, solid colorectal cancer tumors, whereby steps a) to e) according to the first or second aspect of the present invention are performed and repeated over a total treatment period of at least 16 weeks, and whereby no statistically significant progression of said solid tumors is observed between 8 and 16 weeks after initiating treatment. In a fourth aspect of the invention, there is provided a method for retardation or prevention of the progression in a human of right-sided, solid colorectal cancer tumors, which method com- prises performing and repeating steps a) to e) according to the first or second aspect of the present invention, over a total treatment period of at least 16 weeks.

In a preferred embodiment of the fourth aspect, there is provided a method for retardation or prevention of the progression in a human of right-sided, solid colorectal cancer tumors, which method comprises performing and repeating steps a) to e) according to the first or second aspect of the present invention, over a total treatment period of at least 16 weeks, whereby no statistically significant progression of said solid tumors is observed between 8 and 16 weeks after initiating treatment.

During the performance of the follow-up study, ~30% of the patients who had been diagnosed with right-sided CRC and treated according to either the ARFOX protocol or ARFIRI protocol were additionally treated with bevacizumab during some time point in study.

In specific embodiments bevacizumab is administered to a human patient during the treatment period according to any of the aspects of the present invention. In further embodiments, bevacizumab is administered to a human patient at a dose of 5 mg/kg as an IV infusion every two weeks. In still further embodiments, bevacizumab administration is initiated 8 weeks after initiating treatment.

In some embodiments of any of the aspects of the invention, 5-fluorouracil (5-FU) is replaced by a fluorinated pyrimidine base such as capecitabine (Xeloda), ie. N4-pentyloxycarbonyl- 5'-deoxy-5-fluorocytidine, tegafur, 5-fluoro-pyrimidinone, UFT, doxifluridine, 2'-deoxy-5 fluorouridine, 5'-deoxy-5-fluorouridine, 1-(2'-oxopropyl)-5-FU, and alkyl-carbonyl-5-FU, BOF-A2, ftorafur(TS-l), and S-1.

In preferred embodiments of any of the aspects of the invention, [6R]-5,10-methylenetet- rahydrofolate ([6R]-MTHF) is employed as a solid form which is soluble in water, such as a lyophi- lizate or a salt, optionally stabilized by one or more suitable excipients and/or antioxidants such as citric acid or ascorbic acid or salt forms thereof.

In other preferred embodiments of any of the aspects of the invention the lyophilisate of 6R-MTHF is reconstituted in an aqueous media. In other preferred embodiments of any of the aspects of the invention the lyophilisate of 6R-MTHF is prepared from 6R-MTHF hemisulfate salt.

In other preferred embodiments of any of the aspects of the invention the lyophilisate is prepared from 6R-MTHF hemisulfate salt and trisodium citrate dihydrate.

In preferred embodiments of any of the aspects of the invention, the intravenous bolus administration of steps (b), (c) and (e) occur over of a period of 10 minutes or less.

In preferred embodiments of any of the aspects of the invention, the intravenous bolus administration of steps (b), (c) and (e) occur over of a period of 5 minutes or less.

In preferred embodiments of any of the aspects of the invention, the intravenous bolus administration of steps (b), (c) and (e) occur over of a period of 3 minutes or less.

In preferred embodiments of any of the aspects of the invention, step (c) follows step (b) after a period of 30 minutes ± 5 minutes.

In preferred embodiments of any of the aspects of the invention, step (d) follows step (c) after a period of less than 60 minutes.

In preferred embodiments of any of the aspects of the invention, step (d) follows step (c) after a period of between 30 and 60 minutes.

EXAMPLES

Arfolitixorin (former Modufolin®) is a folate-based biomodulator developed by applicant to improve the outcome of a range of antimetabolite treatments used within oncology. One of the therapeutic areas of specific interest included in the development program of arfolitixorin is as biomodulator of 5-fluorouracil (5-FU) activity in standard treatment regime for advanced, metastatic CRC, such as Stage IV.

The drug substance in arfolitixorin is [6R]-5,10-MTHF described hereinabove, which is a stable formulation of the naturally occurring diastereoisomer of MTHF. As mentioned in the background section of the present application, [6R]-5,10-MTHF, shortened [6R]-MTHF, is also a metabolite of leucovorin (LV). Unlike LV, arfolitixorin does not need to undergo metabolism and may be directly involved in the formation of the FdUMP TS ternary complex discussed hereinabove. Clinical Study ISO-CC-005 was an exploratory, Phase l/ll multiple-centre study to be carried out in Stadium IV CRC patients. The study was designed to show clinical relevance for patients by characterizing the tolerability of four arfolitixorin dose levels (30, 60, 120, and 240 mg/m²) in six different standard clinical settings in the presence of fixed doses of 5-FU alone or in combination with either oxaliplatin, irinotecan, or oxaliplatin and bevacizumab. The below Table shows the initial treatment protocol for the Chemotherapy Agents (Bevacizumab, Oxaliplatin, Irinotecan, and/or 5-FU) and of the Study Drug arfolitixorin (Modufolin®):

Table 1

The tolerability of arfolitixorin was to be determined by the presence of Dose Limiting Toxicity (DLT) in each of the treatment arms and for each investigated arfolitixorin dose. For this, the safety of enrolled patients was closely monitored during the study with detailed rules for advancing to next dose cohort(s) or stopping the study.

The study was divided in the Main Study and the Follow-up study. In the Main Study, patients received study treatment with arfolitixorin during eight (8) weeks. Patients eligible for the Follow- up study could participate until reaching progress, but no longer than 18 months.

The Main Study was divided into a dose-finding and a proof-of-concept part. The goal with the Dose-finding Part of the Main Study was to establish the arfolitixorin dose level assessed as having the most favourable profile, i.e. the selected phase 2 dose (SP2D). The goal with the Proof-of- concept Part of the Main Study was to acquire data on the safety and tolerability of arfolitixorin at the SP2D dose level in settings equivalent to the two well-established combination therapies FOLFOX (i.e. oxaliplatin/5-FU/LV) and FOLFIRI (i.e. irinotecan/5-FU/LV).

Enrolled patients, stadium IV CRC patients, were aware of the relatively poor prognosis of their disease. Those patients who could continue benefiting from treatment with a seemly effective therapy, were offered the possibility to continue study treatment by participating in the Follow- up Study. In the Follow-up Study patients continued to receive the same treatment as assigned during the Main Study period. However, the Investigator could complete the allocated treatment with other therapeutic agents of choice in alignment with standard of care in order to adapt treatment to the patient's specific needs and, in this way, provide optimal care.

Response was measured in short- and long-term assessments. During the Main Study phase, only short-term assessments of tumour response were explored by means of objective response rate (ORR) and early tumour shrinkage (ETS). These assessments were to be used as indicators of prognostic factor in ascertaining earlier non responders and to explore the correlation to other factors such as folate levels, tumour biomarkers, or expression levels of certain key genes.

As mentioned hereinabove, during a further analysis of the Follow-up study results applicant has now discovered that some of the tested combinations have proven surprisingly effective in patients diagnosed with right-sided colorectal cancer (RCRC); a cancer type which is notoriously difficult to treat. Some of the treated RCRC patients were further determined by genotype testing to be KRAS- and/or BRAF-mutation positive.

The objectives in the follow-up study were to:

• To characterise all adverse events (AEs) and clinically significant abnormal laboratory test result changes regardless of attribution during the entire Follow-up Study period.

• To evaluate tumour response and disease progression by means of ORR after every response evaluation since treatment allocation in the Main Study and as long patients continue in the Follow-up Study.

• To evaluate tumour response and disease progression by means of PFS and TTP since treatment allocation in the Main Study and until the end of patient participation in the Follow-up Study.

• To evaluate time-to-death since treatment allocation in the Main Study.

• To evaluate the change in tumour biomarker (TK1) levels in blood after every four (4) consecutive cycles of treatment with combination therapy in the subset of patients with available blood samples.

Correlation between tumour biomarkers in blood and treatment response by means of PFS and ORR as per RECIST 1.1 since baseline baseline in the Main Study was determined in in the subset of patients with available blood samples. Similarly, the correlation between tumour biomarkers in tumour tissue and treatment response by means of PFS and ORR as per RECIST 1.1 since baseline in the Main Study, was determined in the subset of patients with available tissue biopsy samples.

In the following, the main results of the follow-up study will be discussed.

RESULTS

See Figure 2 for a summarized overview of the 31 participating patients in the Follow-up study. In the following a more detailed, yet anonymized case narrative is given for each patient up to either 8 or 16 weeks treatment, depending on termination.

Patients had been randomized to either the ARFOX or ARFIRI treatment protocol before the follow-up study started, and remained on this protocol for the duration of the study unless otherwise indicated in the below narratives. Patients showing progressive disease (PD) by CT scanning at 8 weeks were not continued in the extension cohorts for another 8 weeks. Patients showing either partial response (PR) or stable disease (SD) at 8 weeks were as a rule continued for 8 more weeks, and assessed again by CT scanning at approximately 16 weeks (or later), i.e. at the 1^st follow-up visit. Some patients were also continued for more than 16 weeks, but are not reported here.

The dates for individual events like e.g. genotype testing are shown in square brackets [nn].

CASES

Case #1

The patient is a 32-year-old white female randomized for treatment according to the ARFOX protocol (see above).

Medical history findings at enrolment are hysterectomy and partial colectomy but no concomitant medication.

The primary right sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-05-10] shows patient is KRAS mutant and BRAF wildtype, NRAS wildtype. Genotype testing [2019-04-24] shows patient is MSI stable.

Baseline CT [2018-04-30] showed 1 target lesion in the liver (right lobe).

At 8week CT [2018-07-02] the sum of diameter of the target lesion(s) remained (stable disease) and patient was thereby eligible for participation in the follow-up study.

At 1^st follow-up visit [2018-08-27] CT the sum of diameter of the target lesion(s) decreased with 16% (stable disease).

During study participation the following AEs were reported: dry eyes grade 1, fatigue grade 1 and neutrophil count decreased grade 2. The decreased neutrophil count was treated with filgrastim. During the follow-up study bevacizumab was added to the ARFOX treatment.

Case #2

The patient is a 64-year-old white female randomized for treatment according to the ARFOX protocol (see above).

The primary right sided tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2018-07-27] shows patient is KRAS, BRAF and NRAS wildtype.

Baseline CT [2018-07-02] showed 2 target lesions in the liver parenchyma.

At 8week CT [2018-09-26] the sum of diameter of the target lesion(s) increased with 24% and additional lesions were discovered (progressive disease). Case #3

The patient is a 69-year-old white female randomized for treatment according to the ARFOX protocol (see above).

No medical history findings and no concomitant medication at enrolment.

The primary right sided tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2018-09-13] shows patient is KRAS wildtype, BRAF mutant, NRAS wildtype.

Genotype testing [2019-02-14] shows patient is MMR stable.

Baseline CT [2018-07-04] showed 1 target lesion in the liver (segment IV).

At 8week CT [2018-09-21] the sum of diameter of the target lesion(s) increased with 22% and additional lesions were discovered (progressive disease).

No AEs nor concomitant medication reported during study participation.

Case #4

A 85-year-old white female randomized for treatment according to the ARFOX protocol (see above).

The primary right sided tumour has been removed and adjuvant therapy with CAPECITABINE has been given.

Genotype testing [2018-09-13] shows patient is KRAS mutant and BRAF and NRAS wildtype. Baseline CT [2018-08-01] showed 1 target lesion in the left lower lobe of the lung.

At 8week CT [2018-10-08] the sum of diameter of the target lesion(s) decreased with 10% (stable disease) and patient consented to participation in the follow-up study.

At 1^st follow-up visit [2018-11-26] CT the sum of diameter of the target lesion(s) decreased with additional 30% (partial response).

During the follow-up study bevacizumab was added to the ARFOX treatment.

Case #5

The patient is a 69-year-old white female randomized for treatment according to the ARFOX protocol (see above).

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-09-13] shows patient is KRAS mutant and BRAF and NRAS wildtype. Baseline MRI [2018-08-09] showed 1 target lesion in the liver parenchyma.

At 8week CT [2018-11-13] the sum of diameter of the target lesion(s) decreased with 33% (partial responses) and patient consented to participation in the follow-up study.

At 1^st follow-up visit [2019-03-18] CT the sum of diameter of the target lesion(s) decreased with additional 25% (partial response).

Case #6

The patient is a 71-year-old white male randomized for treatment according to the ARFOX protocol (see above).

The primary rectal tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2018-08-24] shows patient is KRAS mutant and MLH1, PMS2 and MSH2 stable. Baseline CT [2018-09-14] showed 1 target lesion in the segment 6/7 of the liver.

At 8week CT [2018-11-05] the sum of diameter of the target lesion(s) decreased with 17% (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-02-15] CT the sum of diameter of the target lesion(s) decrease with additional 25% (partial response).

Case #7

The patient is a 75-year-old white male randomized for treatment according to the ARFOX protocol (see above).

Medical history findings at enrolment are asthma that is treated with Symbicort, and sigmoidectomy. No other concomitant medication.

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-11-06] shows patient is KRAS, BRAF and NRAS wildtype.

Baseline CT [2018-10-12] showed 3 target lesions; 2 in the lung (left and right lower lobe) and 1 in the liver (left lobe).

At 8week CT [2018-12-15] the sum of diameter of the target lesion(s) decreased with 64% (partial responses) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-02-23] CT the sum of diameter of the target lesion(s) increased with 10% (partial response).

During study participation the following AEs were reported: nausea, weight loss and thrombocytopenia, all grade 1. No other concomitant medication during main study in addition to the Symbicort patient had at enrollment in the study. During the follow-up study bevacizumab was added to the ARFOX treatment.

Case #8

The patient is a 62-year-old white male randomized for treatment according to the ARFOX protocol (see above). The only medical history finding at enrolment is right colectomy and no concomitant medication.

The primary right sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-10-16] shows patient is KRAS wildtype, BRAF mutant, NRAS wildtype. Genotype testing [2018-10-24] shows patient is MSI negative.

Baseline CT [2018-10-17] showed 5 target lesions in the liver, lung and tumour deposit.

At 8week CT [2018-12-19] the sum of diameter of the target lesion(s) decreased with 6% (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-03-13] CT the sum of diameter of the target lesion(s) increased with 1% but additional lesions were discovered in the lung (progressive disease).

During main study SAE pulmonary embolism [2019-12-18] was reported.

The following non-serious AEs were reported during main or follow-up: nausea, fatigue, anemia and weight loss.

Bevacizumab treatment was initiated during the follow-up study. Case #9

The patient is a 61-year-old white female randomized for treatment according to the ARFOX protocol (see above). Medical history findings at enrolment are hyperuricemia and hypertension that are both treated.

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-10-17] shows patient is KRAS wildtype, BRAF mutant, NRAS wildtype and MSI negative.

Baseline CT [2018-10-25] showed 3 target lesions in the liver (segment IV, VI and VII).

At 8week CT [2018-12-27] the sum of diameter of the target lesion(s) decreased with 37% (partial response) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-03-06] CT the sum of diameter of the target lesion(s) decrease with 15% but additional lesions were discovered (progressive disease).

The only AE reported during patient's participation in the study was fatigue grade 1. Bevacizumab treatment was initiated during the follow-up study in addition to the concomitant medication patient had at enrollment in the study.

Case #10

The patient is a 48-year-old white male randomized for treatment according to the ARFOX protocol (see above).

The primary rectal tumour is still in place and no adjuvant therapy has been given. Genotype testing [2018-11-26] shows patient is KRAS, BRAF and NRAS wildtype.

Baseline CT+MRI [2018-11-12] showed 3 target lesions; in the liver lobe, in the pericolonic lymph nodes (lymph nodes) and in left pelvis.

At 8week CT [2019-02-09] the sum of diameter of the target lesion(s) decreased with 14% (stable disease) and patient was thereby eligible for participation in the follow-up study.

At 1st follow-up visit [2019-05-02] CT the sum of diameter of the target lesion(s) decreases with additional 59% (partial response).

Case #11

The patient is a 67-year-old white female randomized for treatment according to the ARFOX protocol (see above).

Medical history findings at enrolment are an ostomy surgery in the past and an ongoing Candida infection, but no concomitant medication.

The primary right sided tumour is still in place and no adjuvant therapy has been given. Genotype testing [2018-12-12] shows patient is KRAS and BRAF wildtype, NRAS mutant. Baseline CT [2018-12-16] showed 2 target lesions in the liver (right lobe dorsal lateral). At 8week CT [2019-02-26] the sum of diameter of the target lesion(s) decreased with 40% (partial response) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-04-25] CT the sum of diameter of the target lesion(s) decreased with an additional 29% (partial response).

During study participation the following AEs were reported: dry skin grade 1, treated with Canoderm, ileostomy infection grade 2, treated with antibiotics, insomnia grade 1 and loss of appetite grade 2. Patient also had a number of AEs related to bone marrow toxicity (neutropenia, leukopenia) with grade ranging from 1-3 - treated accordingly with Zarzio, and a couple of occasions of nausea grade 1 despite a number of prophylactic drugs given. During participation patient also developed neuropathy grade 1.

During study participation, patient also received thrombosis prophylaxis and constipation prophylaxis. Patient's Candida infection [MH] was treated with fluconazole and nystimex.

Case #12

The patient is a 69-year-old white male randomized for treatment according to the ARFOX protocol (see above).

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-12-28] shows patient is KRAS and NRAS wildtype.

Baseline CT [2018-12-03] showed 3 target lesions; in the part IV of the liver, in left adrenal gland and in lung nodules. At 8week CT [2019-02-27] the sum of diameter of the target lesion(s) decreased with 36% (partial responses) and patient consented to participation in the follow-up study. At 1st follow-up visit [2019-04-24] CT the sum of diameter of the target lesion(s) decrease with additional 33% (partial response).

Case #13

The patient is a 34-year-old white female randomized for treatment according to the ARFOX protocol (see above).

No medical history findings and no concomitant medication at enrolment.

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2019-01-31] shows patient is KRAS, BRAF and NRAS wildtype.

Baseline MRI [2019-01-02] showed 2 target lesions in the liver (left and right lobe).

At 8week CT [2019-02-28] the sum of diameter of the target lesion(s) decreased with 18% (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-05-13] CT the sum of diameter of the target lesion(s) decreased with an additional 60% (partial response).

No AEs nor concomitant medication reported during main study, but panitimumab was added to the ARFOX treatment during the follow-up study.

Case #14

The patient is a 53-year-old white male randomized for treatment according to the ARFOX protocol (see above).

Medical history finding at enrolment is depression, which is treated with Sobril. Other concomitant medication at enrolment is treatment of pain, heartburn, rhinit as well as constipation and thrombosis prophylaxes.

The primary right sided tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2019-01-09] shows patient is KRAS wildtype, BRAF mutant, NRAS wildtype and MSS negative.

Baseline CT [2019-01-02] showed 3 target lesions in the liver (segment IV and VII) and lymph node. At 8week CT [2019-03-27] the sum of diameter of the target lesion(s) increased with 29% and additional lesions were discovered (progressive disease).

Case #15

The patient is a 68-year-old white male randomized for treatment according to the ARFOX protocol (see above).

The primary right sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2019-01-31] shows patient is KRAS mutant and MSS negative.

Baseline CT [2019-02-21] showed 2 target lesions; in segment 6/7 and segment 8 of the liver. At 8week CT [2019-04-15] the sum of diameter of the target lesion(s) decreased with 53% (partial responses) and patient was thereby eligible for participation in the follow-up study. At 1st follow-up visit [2019-06-12] CT the sum of diameter of the target lesion(s) decrease with additional 30% (partial response).

Case #16

The patient is a 70-year-old white male randomized for treatment according to the ARFOX protocol (see above).

The primary right sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-09-26] shows patient is MSI stable (microsatellite instability absent). Genotype testing [2020-02-04] shows patient is KRAS, BRAF and NRAS wildtype.

Baseline CT [2019-03-06] showed 1 target lesion in the liver.

At 8week CT [2019-06-07] the sum of diameter of the target lesion(s) remained but additional lesions were discovered in the lung (progressive disease).

Case #17

The patient is a 66-year-old white female randomized for treatment according to the ARFOX protocol (see above).

The primary rectal tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2019-01-08] shows patient is KRAS mutant and BRAF and NRAS wildtype.

Baseline CT [2019-03-07] showed 2 target lesions; in the left lower lung lobe and in the right upper lung lobe.

At 8week CT [2019-05-17] the sum of diameter of the target lesion(s) decreased with 12% (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-07-29] CT the sum of diameter of the target lesion(s) remained (stable disease).

Case #18

The patient is a 68-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

Medical history findings at enrolment are depression, gastroesophageal reflux and insomnia which are treated accordingly. Other medical history findings are untreated atrial fibrillation grade 2 and back pain. Patient also has liver surgery and hemicolectomy reported as medical history.

The primary left sided tumour has been removed and adjuvant therapy with FOLFOX [EOT 2017- 01-05] has been given.

Genotype testing shows patient is KRAS wildtype, BRAF mutant, NRAS wildtype.

Baseline MRI [2018-03-06] showed 1 target lesion in the liver (right dorsal).

At 8week MRI [2018-05-28] the sum of diameter of the target lesion(s) decreased with 30% (partial response) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2018-08-15] MRI the sum of diameter of the target lesion(s) decreased with an additional 40% (partial response).

During the study, the patient had severe problems with Gl related toxicity such as nausea and vomiting. Patient was allowed to try Nordic FLIRI regimen (irinotecan 180 mg/m² on day 1, bolus 5-FU 500 mg/m² and leucovorin 60 mg/m² on day 1 and 2) during follow-study without any significant change of toxicity.

Patient also reported a number of occasions of fatigue grade 1-2 during study participation and initially one episode of paroxysmal atrial fibrillation grade 3 and a month later atrial fibrillation grade 3 - both reported to be related to the study drug by the investigator.

During follow-up study the patient twice receives radiotherapy due to AE costal pain.

Case #19

The patient is a 65-year-old white female randomized for treatment according to the ARFIRI protocol (see above).

The primary rectal tumour is still in place and adjuvant therapy with CAPECITABINE-OXALIPLATIN [EOT 2016-01-29] has been given.

Genotype testing [2018-03-22] shows patient is KRAS, BRAF and NRAS wildtype.

Baseline CT [2018-03-27] showed 1 target lesion in the pelvis (cervix, near rectal stump).

At 8week CT [2018-06-22] the sum of diameter of the target lesion(s) remained (stable disease) and patient was thereby eligible for participation in the follow-up study.

At 1st follow-up visit [2018-09-03] CT the sum of diameter of the target lesion(s) remained (stable disease).

Patient terminated study due to AE 'Thromboembolic event' [2018-09-03] after 1st follow-up visit.

During the follow-up study bevacizumab was added to the ARFIRI treatment.

Case #20

The patient is a 74-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

Medical history findings at enrolment are hypertension that is treated accordingly, hyperlipidemia and a right hemicolectomy. Patient is treated with Salospir and Placol as cardiovascular prevention.

The primary right sided tumour has been removed and adjuvant therapy with CAPECITABINE- OXALIPLATIN [EOT 2017-UNK-UNK] has been given.

Genotype testing [2018-05-04] shows patient is KRAS, BRAF and NRAS wildtype. Baseline CT [2018-05-14] showed 5 target lesions in the lung (right and left lobe), abdomen and abdominal aorta.

At 8week CT [2018-07-10] the sum of diameter of the target lesion(s) decreased with 27% (stable disease) and patient was thereby eligible for participation in the follow-up study.

At 1st follow-up visit [2018-08-31] CT the sum of diameter of the target lesion(s) decreased with an additional 10% (partial response).

Patient terminated study due to PI decision due to maximum clinical benefit [2018-10-05], The only AE reported was a diarrhea grade 1 during follow-up study and during the follow-up study bevacizumab was added to the ARFIRI treatment. No other concomitant medication in addition to the concomitant medication patient had at enrollment in the study.

Case #21

The patient is a 67-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

The primary left sided tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2018-05-22] shows patient is KRAS mutant, BRAF wildtype and MLH1, PMS2, MSH2 and MSH6 stable.

Baseline CT [2018-04-16] showed 3 target lesions in the liver; 1 in left lobe apical and 2 in right lobe.

At 8week CT [2018-07-09] the sum of diameter of the target lesion(s) decreased with 42% (partial responses) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2018-10-17] CT the sum of diameter of the target lesion(s) decreased with additional 43% (partial response).

Case #22

The patient is a 58-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2017-11-28] shows patient is KRAS mutant and BRAF and NRAS wildtype. Baseline CT [2018-07-23] showed 2 target lesions in the lung; right lower lobe and lymphnode. At 8week CT [2018-09-26] the sum of diameter of the target lesion(s) remained (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2018-12-13] CT the sum of diameter of the target lesion(s) remained (stable disease).

During the follow-up study bevacizumab was added to the ARFIRI treatment.

Case #23

The patient is a 68-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

Medical history findings at enrolment are hypertension and restless legs that are treated accordingly. At enrolment, a Peripherally inserted central catheterization is done. No other concomitant medication. The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-08-10] shows patient is KRAS wildtype, BRAF wildtype and MLH1, PMS2, MSH2 and MSH6 stable.

Baseline MRI [2018-07-06] showed 2 target lesions in the liver (segment 1 and 7).

At 8week MRI [2018-10-01] the sum of diameter of the target lesion(s) decreased with 13% (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-01-10] MRI the sum of diameter of the target lesion(s) decrease with an additional 20% (stable disease).

During the first 8 weeks of study participation the following AEs were reported: hypotension grade 2, insomnia grade 1 and worsening of restless legs (grade 1) that was reported as medical history.

Beside treatment of the AEs reported, patient also received constipation prophylaxis, thrombosis prophylaxis and nausea prophylaxis.

Case #24

The patient is a 58-year-old white female randomized for treatment according to the ARFIRI protocol (see above).

Medical history findings at enrolment are depression and pain that are treated accordingly. Other medical history findings are twisted ovarian cyst, struma [goitre], anorexia, rash, fatigue and dry mouth. Medication for rash is prescribed at enrolment.

The primary right sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2018-07-31] shows patient is KRAS mutant and BRAF wildtype, NRAS wildtype. Baseline CT [2018-08-22] showed 2 target lesions in retroperitoneal lymph node.

At 8week CT [2018-10-22] the sum of diameter of the target lesion(s) decreased with 47% (partial response) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2018-12-17] CT the sum of diameter of the target lesion(s) decreased with an additional 32% (partial response).

Dizziness grade 1 and nausea grade 1 are reported at almost every treatment cycle, and nausea is treated with both oral an i.v. nausea prophylaxis. Patient also reports several episodes of epistaxis grade 1. Dry skin grade 1 is reported a couple of times and so is pain grade 1, lasting for several weeks at a time. During follow-up study oral mucositis lasting for more than a month is reported, treated with chamomile flower tea.

Case #25

The patient is a 65-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2017-10-12] shows patient is KRAS mutant and BRAF wildtype. Genotype testing [2017-10-13] shows patient is MSI negative.

Baseline CT [2018-08-23] showed 1 target lesion in segment VI of the liver.

At 8week CT [2018-10-31] the sum of diameter of the target lesion(s) remained (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-01-09] CT the sum of diameter of the target lesion(s) remained but additional lesions were discovered (progressive disease). Case #26

The patient is a 63-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

The primary right sided tumour has been removed but no adjuvant therapy has been given.

No genotype testing performed.

Baseline CT [2018-10-29] showed 2 target lesions; left ventral (gland) and left aorta (gland).

At 8week CT [2018-12-18] the sum of diameter of the target lesion(s) decreased with 54% (partial response) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-02-20] CT the sum of diameter of the target lesion(s) decreased with additional 8% (partial response).

Case #27

The patient is a 45-year-old white male randomized for treatment according to the ARFIRI protocol (see above).

The primary right sided tumour has been removed and adjuvant therapy with FLOX [EOT 2017- 06-29] has been given.

Genotype testing [2018-08-06] shows patient is KRAS mutant and MLH1, PMS2, MSH2 and MSH6 stable.

Baseline CT [2018-12-07] showed 1 target lesion the right lower lobe of the lung, ventral.

At 8week CT [2019-02-11] the sum of diameter of the target lesion(s) remained (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-05-20] CT the sum of diameter of the target lesion(s) increased with 50% (progressive disease).

Case #28

The patient is a 46-year-old Asian female randomized for treatment according to the ARFIRI protocol (see above).

The primary rectal tumour is still in place and no adjuvant therapy has been given.

Genotype testing [2018-11-16] shows patient is KRAS and BRAF wildtype and NRAS mutant. Baseline CT [2018-12-27] showed 2 target lesions in the liver.

At 8week CT [2019-04-08] the sum of diameter of the target lesion(s) increased with 80% (progressive disease).

Case #29

The patient is a 72-year-old white female randomized for treatment according to the ARFIRI protocol (see above).

Medical history finding at enrolment is (mild) hypertension treated with hydrochlorothiazide. No other medical history finding nor concomitant medication.

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2019-03-01] shows patient is KRAS and BRAF mutant, NRAS mutant.

Genotype testing [2019-12-12] shows patient is MSI stable (microsatellite instability absent). Baseline CT [2019-03-19] showed 1 target lesion in the lung (left upper lobe). At 8week CT [2019-05-11] the sum of diameter of the target lesion(s) remained (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-07-19] CT the sum of diameter of the target lesion(s) decreased with 44% (partial response).

No AEs and no other concomitant medication in addition to the concomitant medication patient had at enrollment in the study.

Case #30

The patient is a 68-year-old white female randomized for treatment according to the ARFIRI protocol (see above).

Medical history findings at enrolment are hypercholesterolemia, paroxysmal atrial tachycardia and chronic respiratory failure which are treated accordingly.

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2019-04-11] shows patient is BRAF mutant and MSI stable (microsatellite instability absent).

Genotype testing [2019-04-16] shows patient is KRAS wildtype.

Genotype testing [2019-04-19] shows patient is NRAS wildtype.

Baseline CT [2019-04-03] showed 3 target lesions in the liver (right lobe) and lung (right lobe).

At 8week CT [2019-06-04] the sum of diameter of the target lesion(s) decreased with 54% (partial response) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-08-02] CT the sum of diameter of the target lesion(s) decreased with an additional 39% (partial response).

Two AEs are reported during follow-up study; diarrhea and fatigue grade 2. No other concomitant medication in addition to the concomitant medication patient had at enrollment in the study.

Case #31

The patient is a 52-year-old white female randomized for treatment according to the ARFIRI protocol (see above).

No medical history findings and no concomitant medication at enrolment.

The primary left sided tumour has been removed but no adjuvant therapy has been given. Genotype testing [2019-04-25] shows patient is KRAS and BRAF mutant, NRAS wildtype. Genotype testing [2019-04-19] shows patient is MSI stable (microsatellite instability absent). Baseline CT [2019-03-13] showed 2 target lesions in the lung (left and right lower lobe).

At 8week CT+MRI [2019-06-06] the sum of diameter of the target lesion(s) decreased with 15% (stable disease) and patient consented to participation in the follow-up study.

At 1st follow-up visit [2019-07-29] CT the sum of diameter of the target lesion(s) increased with 3% (stable disease).

Patient terminated study due to patient's request [2019-08-06], No AEs nor concomitant medication reported during study participation.

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9. Van Cutsem et al. Fluorouracil, leucovorin, and irinotecan plus cetuximab treatment and RAS mutations in colorectal cancer. J. Clin Oncol. (2015) 33:692- 700

10. KM Tveit et al. Phase III trial of cetuximab with continuous or intermittent fluorouracil, leucovorin, and oxaliplatin (Nordic FLOX) versus FLOX alone in first- line treatment of metastatic colorectal cancer: the NORDIC-VII study J. Clin Oncol. (2012) 30(15):1755-1762)

11. BM Wolpin et al. Systematic treatment of colorectal cancer. Gastroenterol. 2008;134(5):1296 1310 12. H Brenner et al. Colorectal cancer. Lancet. 2014;383(9927):1490-1502. 13. Peng et al. Right- and left-sided stage III colon cancers present different prognostic outcomes of oxaliplatin-based adjuvant chemotherapy after curative resection. Cancer Management and Research 2018:10 14. FA Sinicrope et al. Prognostic Impact of Deficient DNA Mismatch Repair in Patients With Stage III Colon Cancer From a Randomized Trial of FOLFOX-Based Adjuvant Chemotherapy. J Clin Oncol. 2013;31(29):3664-3672. 15. C Cremolini et al. When to Use Triplet Chemotherapy as First-Line Treatment in Metastatic Colorectal Cancer. Clinical Advances in Hematology & Oncology August 2019 - Volume 17, Issue 8 16. C Cremolini et al. Individual Patient Data Meta-Analysis of FOLFOXIRI Plus Bevacizumab Versus Doublets Plus Bevacizumab as Initial Therapy of Unresectable Metastatic Colorectal Cancer. Journal of Clinical Oncology 38(28) August 2020 17. M SIDERIS et al. BRAF V600E Mutation in Colorectal Cancer Is Associated with Right- sided Tumours and Iron Deficiency Anaemia. ANTICANCER RESEARCH 35: 2345-2350 (2015) 18. P Ross Right versus left-sided colon cancer: Is it time to consider these as different diseases? AIMS Medical Science, 5(3): 303-315 (2018) 19. D Hanna, How We Treat Left-Sided vs Right-Sided Colon Cancer. Clinical Advances in Hematology & Oncology Volume 18, Issue 5 May 2020 20. H Taniguchi et al. Tumor Location Is Associated With the Prevalence of Braf And Pik3ca Mutations in Patients with Wild-Type Ras Colorectal Cancer: A Prospective Multi-Center Cohort Study in Japan. Translational Oncology 13 (2020) 100786 21. Li et al. Gastroenterology Report, 8(3), 2020, 192-205 22. Greystoke et al. How Many Diseases Are Colorectal Cancer? Gastroenterology Research and Practice, Vol. 2012, p. 1-12 23. Gomez et al. Anatomical distribution of colorectal cancer over a 10 year period in a district general hospital: is there a true "rightward shift?" Postgrad Med J 2004;80:667- 669 24. Grassadonia et al. Impact of primary tumor location in patients with RAS wild-type metastatic colon cancer treated with first-line chemotherapy plus anti-EGFR or anti- VEGF monoclonal antibodies: a retrospective multicenter study. Journal of Cancer 2019, Vol. 10, 5926 25. Recio-Boiles A, et al. Rectal Cancer. [Updated 2020 Dec 17], In: StatPearls [Internet], Treasure Island (FL): StatPearls Publ. 2021. Available from: https://www.ncbi.nlm.nih.gov/books/NBK493202/ 26. Sun, De., et al. KRAS mutation and primary tumor location do not affect efficacy of bevacizumab-containing chemotherapy in stagae IV colorectal cancer patients. Sci Rep 7, 14368 (2017). 27. Koumarianou A et al., Implications of KRAS status in first line chemotherapy with bevacizumab in advanced colorectal cancer: A phase IV study of Hellenic Oncology Research Group (HORG). Journal of Clinical Oncology 2018 36:15_suppl, el5521-el5521 28. Sanford N et al., Early-onset colorectal cancer: more than one side to the story. COLORECTAL CANCER VOL 9, NO. 3 (2020) 29. Burge M et al., First-line therapy for metastatic colorectal cancer: Current perspectives and future directions. Asia-Pac J Clin Oncol. 2019;15(Suppl. 1):3-14. 30. Giuliani et al., Int J Colorectal Dis. 2018 Nov; 33(11): 1505-1516 (2018) 31. A Venook et al., Impact of primary (

) tumor location on overall survival (OS) and progression-free survival (PFS) in patients (pts) with metastatic colorectal cancer (mCRC): Analysis of CALGB/SWOG 80405 (Alliance). Journal of Clinical Oncology 34, no. 15_suppl (May 20, 2016) 3504-3504. 32. T Sagawa et al., Clinical impact of primary tumour location, early tumour shrinkage, and depth of response in the treatment of metastatic colorectal cancer with first-line chemotherapy plus cetuximab or bevacizumab. Scientifc Reports | (2020) 10:19815 | https://doi.org/10.1038/s41598-020-76756-1

Claims

1) [6R]-5,10-methylenetetrahydrofolate for use in a human patient in the treatment of solid colorectal cancer tumors, which treatment comprises the following steps: a) administering a continuous IV infusion containing either i. 85 mg/m² (of BSA) oxaliplatin, or ii. 180 mg/m² (of BSA) irinotecan, followed by b) administering an IV bolus containing 400 mg/m² (of BSA) 5-fluorouracil, followed by c) administering an IV bolus containing 60 mg/m² [6R]-5,10-methylenetetrahydrofolate, followed by d) administering a continuous IV infusion containing 2400 mg/m² 5-fluorouracil over 46 hours, followed by e) administering an IV bolus containing 60 mg/m² (of BSA) [6R]-5,10-methylenetetrahy- drofolate, wherein the location of the primary tumor of said patient has been determined to be right-sided, and wherein all steps a) - e) are repeated every 2 weeks until termination of the treatment.

2) [6R]-5,10-methylenetetrahydrofolate for use in a human patient in the treatment of solid colorectal cancer tumors according to claim 1, wherein steps a) - e) are repeated every 2 weeks for a total treatment period of at least 16 weeks.

3) [6R]-5,10-methylenetetrahydrofolate for use in a human patient in the treatment of solid colorectal cancer tumors according to claim 1 or 2, wherein the primary tumor of said patient has been determined to be located in the cecum, ascending colon, hepatic flexure and/or transverse colon.

4) [6R]-5,10-methylenetetrahydrofolate for use in a human patient in the treatment of solid colorectal cancer tumors according to any of the preceding claims wherein the human patient has been found by genotype testing to be either KRAS mutation-positive, BRAF mutation positive or both KRAS mutation-positive and BRAF mutation positive.

5) [6R]-5,10-methylenetetrahydrofolate for use in a human patient in the treatment of solid colorectal cancer tumors according to claim 4, wherein genotype testing is performed by dPCR analysis of tumor tissue. 6) [6R]-5,10-methylenetetrahydrofolate for use in a human patient in the treatment of solid colorectal cancer tumors according to claim 4, wherein genotype testing is performed by ctDNA analysis.

7) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human patient of solid colorectal cancer tumors according to any one of the preceding claims wherein bevacizumab is administered during the treatment period.

8) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human patient of solid colorectal cancer tumors according to claim 7, wherein 5 mg/kg bevacizumab is administered as an IV infusion every two weeks.

9) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human patient of solid colorectal cancer tumors according to claim 7 or 8 wherein bevacizumab administration is initiated 8 weeks after initiating treatment.

10) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human of solid colorectal cancer tumors according to any one of the preceding claims wherein the [6R]-5,10-methylene- tetrahydrofolate is employed as a solid form which is soluble in water, such as a lyophilisate or a salt, optionally stabilized by one or more suitable excipients and/or antioxidants such as citric acid or ascorbic acid or salt forms thereof.

11) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human of solid colorectal cancer tumors according to any one of the preceding claims wherein the [6R]-5,10-methylene- tetrahydrofolate has a diastereomeric purity of >98% d.e.

12) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human of solid colorectal cancer tumors according to any one of the preceding claims wherein the intravenous (IV) bolus administration of steps (b), (c) and (e) occur over of a period of 10 minutes or less.

13) [6R]-5,10-methylene-tetrahydrofolate for use in the treatment in a human of solid colorectal cancer tumors according to any one of the preceding claims wherein 5-fluorouracil (5-FU) is replaced by a fluorinated pyrimidine base such as capecitabine (Xeloda), ie. N4- pentyloxycarbonyl-5'-deoxy-5-fluorocytidine, tegafur, 5-fluoro-pyrimidinone, UFT, doxifluridine, 2'-deoxy-5 fluorouridine, 5'-deoxy-5-fluorouridine, 1-(2'-oxopropyl)-5-FU, and alkyl-carbonyl-5-FU, BOF-A2, ftorafur(TS-1), and S-1. 14) [6R]-5,10-methylene-tetrahydrofolate for use in the retardation or prevention of the progression in a human patient of solid colorectal cancer tumors, wherein the location of the primary tumor of said patient has been determined to be right-sided, which comprises performing and repeating steps a) to e) according to any one of the preceding claims over a total treatment period of at least 16 weeks. 15) [6R]-5,10-methylene-tetrahydrofolate for use in the retardation or prevention of the progression in a human patient of solid colorectal cancer tumors according to any one of claim 11 or 12, whereby steps a) to e) according to any one of claims 1-10 are performed and repeated over a total treatment period of at least 16 weeks, and whereby no statistically significant progression of said solid tumors is observed 16 weeks after initiating treatment.