5-methyltetrahydrofolate or 5-formyltetrahydrofolic acid to modulate 5-fluorouracil's cytotoxic activity in vivo. A phase II study in patients with advanced colon cancer

The purpose of this study was to test the hypothesis that 5-methyltetrahydrofolate (Me-THF), a source of reduced folates alternative to leucovorin, could effectively modulate 5-fluorouracil's (5-FU) cytotoxic activity in patients with advanced colon cancer. A total of 23 patients were enrolled in a phase 11 trial; they received 5-FU as a 30-min infusion at a dose of 370 mg/m2 following a rapid i.v. push of 200 mg/m2 Me-THF, both drugs being given for 5 consecutive days. Cycles were repeated every 4 weeks until disease progression. No patient achieved a complete response. In all, 4 patients showed a partial response (17.4%), 7 developed stable disease (30.4%), and the remaining 12 (52.2%) progressed. Toxicity was acceptable and never exceeded WHO grade III intensity. According to our experience, the MeTHF/5-FU combination does not appear to be an effective treatment for advanced colon cancer. Despite its low toxic profile, in our opinion its wider use should be discouraged.