A drug used to treat cancers of the breast, colon, rectum, stomach, and pancreas. It is used under the brand names Carac, Tolak, Efudex, and Fluoroplex as a cream to treat actinic keratosis (a skin condition that may become cancer). It is also used under the brand name Efudex as a cream to treat basal cell skin cancer that is superficial (not invasive) and cannot be treated with other therapy. Fluorouracil is being studied in the treatment of other conditions and types of cancer. It stops cells from making DNA and may kill cancer cells. Fluorouracil is a type of antimetabolite. Also called 5-fluorouracil and 5-FU.