5-fluorouracil (5-FLOOR-oh-YOOR-uh-sil) is 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. 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. Also called 5-FU and fluorouracil.