Evaluation of the carcinogenic effects of estrogens, progestins and oral contraceptives on cervix, uterus and ovary of animals and man.

Estrogens do not have the general biological effect of increasing the occurrence of cancer in various species of laboratory animals. The neoplastic effect of estrogens in animals is strain and species dependent. Estrogens may increase the incidence of uterine cervical cancer in some strains of mice, but not in other strains or other animal species. The progestins and oral contraceptives (OC) have not induced cervical cancer in animals and most studies demonstrate that the steroid anovulants do not increase the occurrence of abnormal cervical smears or cervical cancer in women. Estrogens increase the occurrence of endometrial cancer in the rabbit, occasionally in the mouse, but apparently not in other species. Case-control studies in menopausal and postmenopausal women indicate an increased risk of endometrial carcinoma (EC) associated with use of estrogen. However, in other studies estrogen has not been related to EC. Cases of EC have been reported in women using sequential OC but a causal relationship has not been established. Progestins alone may arrest progress or cause regression of EC in women. EC has not been related to use of the combination OC, and it is unlikely that use of these anovulants will lead to the development of endometrial cancer. Estrogens or OC do not induce a carcinogenic response in the ovary. A decrease in ovarian cysts, is observed during the clinical use of OC.