Postmenopausal hormone replacement therapy and breast cancer

The concern that postmenopausal hormone replacement therapy (HRT) may cause cancer of the breast has generated much research in epidemiology, endocrinology, and tumor cell biology. The recognition that naturally occurring 17beta-estradiol is a weak genotoxic and mutagenic carcinogen provides a plausible background for the association of breast cancer with HRT. However, because of the small anticipated effect and several confounding factors, the epidemiology of this association is complex. The consensus at this writing is that long-term HRT (>10 years) is associated with an increased risk of breast cancer, which, on average, is equivalent to the risk associated with delaying menopause for the same period of time. The particular risk depends on the duration and probably the dose to which the individual woman is exposed, as well as on a number of predisposing environmental and genetic factors. One clinical implication of the data reviewed here is that the dosage of HRT chosen should be the lowest that produces the desired effect. The use of HRT in women with a history of breast cancer is also addressed. Low-dose estrogen together with a selective estrogen receptor modulator to protect the breast may be a treatment option for women with severe symptoms of estrogen deficiency.