Effect of 5-Fluorouracil on Early Teratomas in Mice¹

Testicular teratomas were experimentally induced in Strain 129/Sv mice by grafting genital ridges from 12-day fetuses into the testes of adults. In approximately 80% of the grafts a teratocarcinogenetic process was initiated within 24 hr. The tumors grew and were composed predominantly of neural tissue. This provided a well-defined oncogenic system in which to study the carcinostatic effects of compounds such as 5-fluorouracil (FU). Host mice received a single injection of FU at 50 mg/kg on one of several days beginning with the day prior to grafting and ending with the 11th day following grafting. The development of teratomatous foci was markedly inhibited in grafts in mice treated on Days 1 through 6. Those in hosts treated on Days 7 through 11 had an increasing incidence of tumors approaching that of the controls (78%). FU at 25 mg/kg also prevented the growth of tumors when injected into host mice on Day 0 or Day 1.