Effects of Conjugated Estrogens with or without Medroxyprogesterone Acetate on Mammary Carcinogenesis, Uterine Adenomyosis and Femur in Mice

Although combined hormone replacement therapy using estrogens and progestins reduces the risk of endometrial cancer in postmenopausal women, it has been unclear whether the combined therapy is associated with an alteration of the risk of mammary cancer. Virgin mice of the SHN strain, which has a high potential for the development of mammary cancer and uterine adenomyosis, were given diets containing conjugated estrogens with or without medroxyprogesterone acetate for 230 days. The combined administration of conjugated estrogens and medroxyprogesterone acetate completely suppressed the development of uterine adenomyosis with a decrease in uterine thymidylate synthetase activity, significantly enhanced the bone mineral density in the femur and slightly shortened the latent period of mammary carcinogenesis.