Total suppression of spontaneous endometrial carcinoma in BDII/Han rats by melengestrol acetate

Female virgin BDII/Han rats develop spontaneous endometrial carcinoma (EC) in incidences up to 90%. Our objective was to determine whether lifelong administration of the progestin melengestrol acetate (MGA) would suppress those tumors. Four groups of 20 rats aged 24-28 days were employed Group I animals were untreated controls. Groups II, III, and IV were fed 0.1, 0.2, and 0.4 mg MGA/kg daily in their diet during their lifetimes. All treated groups were free from EC during their lifetimes with an increased lifespan up to 30%. The controls, in contrast, had an EC incidence of 85%. Histologically, with one exception all tumors were classified as adenocarcinoma. While most of the control rats died from EC, nearly all animals of groups II and III died from age-related diseases. Rats in group IV showed side effects due to the glucocorticoid properties of MGA. Besides alopecia and obesity an acceleration of chronic progressive nephrosis was observed. The study establishes the validity of the prophylactic approach to spontaneous hormone-dependent cancers in a rat tumor model.