Breast cancer risk with oral contraceptives and oestrogen replacement therapy.

A detailed review of the international epidemiological literature is very reassuring in confirming that exogenous oestrogen in oral contraceptives and postmenopausal hormone replacement therapy does not induce breast cancer in women. However, there may sometimes be a promotional effect which accelerates the time of breast cancer diagnosis in certain subgroups of women. This promotional effect may occur in young oral contraceptive users, and in long term users of high dose oestradiol postmenopausal replacement formulations. Use of oral contraceptives while young may protect against the development of breast cancer after age 45. Physiological doses of conjugated equine oestrogens do not appear to increase breast cancer risk even with long-term postmenopausal use. Current data do not support an effect of progestogens in increasing or decreasing risk of breast cancer.