A drug used to treat cancers of the breast, colon, rectum, stomach, and pancreas. Under the brand names Carac, Tolak, Efudex, and Fluoroplex, it is used 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 removed by surgery. 5-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. 5-fluorouracil is a type of antimetabolite.