Prevention and delay of spontaneous mammary and pituitary tumors by long- and short-term ingestion of 5-fluorouracil in Wistar-Furth rats.

Ingestion of 5-fluorouracil at 17 mg/kg/day by female retired breeders of the Wistar-Furth strain of rats beginning at 11 1/2 and extending to 30 months of age prevented the appearance of a significant number of palpable mammary tumors and a highly significant number of spontaneous pituitary tumors in animals which reached the age of 30 months. Also, short-term toxic regimens of 65 mg/kg/day for 3 1/2 days and 34 mg/kg/day for three 5-day periods at intervals of 5 days, used to determine effects upon mammary tumors only, both delayed but did not prevent the eventual occurrences of the expected number of mammary tumors by 30 months of age. The possibility of 5-FU playing a role in protection against environmental carcinogens is suggested.