PROBLEM TO BE SOLVED : To provide methods for treating solid tumors such as cancer. SOLUTION : Disclosed is a method comprising the following regimen a) to e) : a) on Day 1, administering an IV bolus containing 10-1000 mg/m2 (BSA) of 5-FU; then b) either simultaneously or after a period of from 10 min to 4 hours, administering two or more IV boluses, each containing 5-1000 mg/m2 of [6R]-5, 10-methylenetetrahydrofolate ([6R]-MTHF) interspaced by a period of 10-60 minutes; c) administering a continuous infusion of 5-FU over a period of 46 hours, or until the end of Day 2; d) optionally administering one IV bolus containing 5-1000 mg/m2 (BSA) of [6R]-MTHF before the end of Day 1; e) on Day 2, optionally administering one or more IV boluses each containing 5-1000 mg/m2 of [6R]-MTHF. SELECTED DRAWING : Figure 2 COPYRIGHT : (C)2019, JPO&INPIT