The present invention relates to methylene-tetrahydrofolate for use in the treatment of cancer, based on its 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, mesothelioma cancer, lung cancer including non-small-cell lung cancer, ovarian cancer, endometrial cancer, cervical cancer, peripheral cell lymphoma (PTCL), melanoma, brain tumors, adenocarcinoma, esophageal cancer, and osteosarcoma.
