Induction of mammary adenocarcinomas by medroxyprogesterone acetate in BALB/c female mice.

In a previous paper we reported that medroxyprogesterone acetate (MPA) decreased the incidence of foreign body tumorigenesis in BALB/c mice but that mammary adenocarcinomas appeared in some of the females. The experiment was repeated in 245 virgin females as follows: (1) 40 mice treated with 40 mg of MPA depot s.c. every 2 months during a whole year; (2) 117 mice bearing a foreign body (FB) and treated with MPA; (3) 46 mice bearing a FB; (4) 42 non-treated mice. Mammary adenocarcinomas developed in 16/40 in group 1 and 30/117 in group 2; no mammary tumors appeared in either control groups. The tumors were infiltrating adenocarcinomas often affecting more than one mammary gland; metastases were occasionally observed. Animals killed after 1 year of MPA treatment presented deciduomas. MPA also decreased the incidence of FB-induced sarcomas, confirming previous results.