The present invention relates to the use of reduced folates such as methylene-tetrahydrofolate, tetrahydrofolate or methyl-tetrahydrofolate for use in the treatment of cancer, based on their intrinsic antitumor activity. The cancers that may be treated include breast cancer, gastric cancer, gastrointestinal cancer, gall bladder cancer, bile duct cancer, colon cancer, rectal cancer, liver cancer, pancreatic cancer, head and neck cancer, esophageal cancer, mesotheolioma cancer, lung cancer including non-small-cell lung cancer, ovarian cancer, endometrial cancer, cervicial cancer, peripheral T-cell lymphoma (PTCL), melanoma, brain tumors, adenocarcinoma, esophageal cancer, and osteosarcoma.
