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 l ifelong administration of the progestin melengestrol acetate (MGA) wou ld 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 th eir lifetimes. All treated groups were free from EC during their lifet imes with an increased lifespan up to 30%. The controls, in contrast, had an EC incidence of 85%. Histologically, with one exception all tum ors were classified as adenocarcinoma. While most of the control rats died from EC, nearly all animals of groups II and III died from age-re lated diseases. Rats in group IV showed side effects due to the glucoc orticoid properties of MGA. Besides alopecia and obesity an accelerati on of chronic progessive nephrosis was observed. The study establishes the validity of the prophylactic approach to spontaneous hormone-depe ndent cancers in a rat tumor model.