5-Fluorouracil treatment of rat leukemia and a reappraisal of its application in human leukemia.

5-Fluorouracil (5-FU), an effective pyrimidine antimetabolite was evaluated in the BNML rat model of human acute myeloid leukemia. Single injections of 5-FU, 15-50 mg/kg i.p., caused a sharply dose-related reduction of leukemic growth as measured by liver and spleen weights and leucocyte counts. Similar results were obtained with three doses of 5-FU over a period of 10 days. No apparent toxicity was observed in these experiments. A schedule of 25 mg/kg every 5 days extended the survival time of leukemic rats to 156%, as compared to untreated controls. In the BNML model such an increase in lifespan is equivalent to a 10,000 fold reduction of the tumor mass. These results indicate a potential value of 5-FU treatment in human myeloid leukemia. 5-FU, however, is not used in the clinical treatment of leukemia. A review of the literature revealed that there have been very few relevant studies of this application of 5-FU, while the more unique activity of this drug against some solid tumors has been investigated extensively. Therefore, it can be concluded that there is no clear evidence of the ineffectiveness of 5-FU against leukemia, and that further investigations should find out whether the disregard of 5-FU in this respect is justified.