Effect of prenatal treatment with ethinyl estradiol on the mouse uterus and ovary.

Oral ethinyl estradiol (0.01 or 0.02 mg. per kilogram) administered prenatally to ICR-JCL strain mice before the development of the uterine and ovarian blastemata induced cystic glandular hyperplasia with epidermization in the endometrium and excessive formation of degenerating follicles in the ovaries at 10 to 14 weeks of age. To the evidence for the production by estrogen of malignant uterine neoplasms in rodents and the clinical data showing that cystic glandular hyperplasia develops after prolonged estrogen administration in postmenopausal women and adenocarcinoma in premenopausal or menopausal women using oral contraceptives including ethinyl estradiol, we add the present results which suggest that ethinyl estradiol administered transplacentally can cause malignant transformation of the uterine endometrium in mice.