A drug used to treat cancers of the breast, stomach, and pancreas, and certain types of colorectal and head and neck cancers. It is also used in a cream to treat basal cell skin cancer and actinic keratosis (a skin condition that may become cancer). It is being studied in the treatment of other conditions and types of cancer. Fluorouracil stops cells from making DNA and it may kill cancer cells. It is a type of antimetabolite. Also called 5-fluorouracil, 5-FU, Adrucil, Efudex, and Fluoroplex.