Experimental Studies on the Mechanisms oe the Antineoplastic Activity of Medroxyprogesterone Acetate.

The mechanism of the antineoplastic action of medroxyprogesterone acetate (MPA) is not completely clear. It is probably related at least in part, to an antiestrogenic activity of the progestin which is obtained in different ways (Hsueh et al. 1, Di Carlo et al. 2, Di Carlo et al. 3, Hellman et al. 4). Studies from Cho-Chung et al. 5, 6 have demonstrated an antagonistic action between cAMP and estrogen in DMBA - induced mammary tumor growth control. The same Authors have also observed that the mammary tumor regression induced by tamoxifen and high doses of estrogen proceeds through a series of cAMP mediated events (Bodwin et al. 7). The aim of this investigation was to study the effects of MPA on DMBA-induced rat mammary tumor growth and the correlation (if any) between tumor regression and estrogen receptor levels (ER), cAMP levels and phosphodiesterase activity (PDE).