ESTROGEN AND PROGESTIN EFFECTS IN HUMAN BREAST CARCINOGENESIS

The influences of estrogen and progestin on human mammary neoplasia ar e reviewed with a view to identifying what is known about their effect s. Estrogens promote growth of established cancer and pharmacological levels of progestins induce remission. In vivo, highest proliferation of histologically normal mammary epithelium occurs in the progestogeni c phase of the menstrual cycle or under the progestogenic influence of oral contraceptives. Little additional hard data exist to indicate wh ether progestins promote or inhibit human mammary carcinogenesis. Effe cts on proliferation, steroid receptor content and development are dis cussed together with interpretation of epidemiological data on risk fa ctors that have hormonal components. Progestins may not be the benign or beneficial agents previously supposed, and there are virtually no d ata to suggest that they are antiestrogenic. It is hypothesized that c arcinogenesis may be accompanied by increased sensitivity to estrogen, which provides a growth advantage to the tumor by maximizing use of t he low estrogen concentrations encountered in the postmenopausal state .