A drug given as an injection to treat cancers of the breast, colon, rectum, stomach, and pancreas and as a cream to treat actinic keratosis (a skin condition that may become cancer) and certain types of basal cell skin cancer. It is used under the brand names Carac, Tolak, Efudex, and Fluoroplex to treat actinic keratosis. It is also used under the brand name Efudex to treat basal cell skin cancer. 5-fluorouracil is also 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. Also called 5-FU and fluorouracil.