[Hormone therapy of menopause and risk of breast cancer. Polemics and controversies].
The risk/benefit ratio of hormone replacement therapy in the post-menopause period remains controversial due to the risk of breast cancer and the effects of progesterone on mammary tissues. We analyzed the epidemiological data available to evaluate the risk of breast cancer in subjects taking replacement hormones. Oestrogen prescribed alone has not been reported to increase the relative risk of breast cancer compared with subjects not taking hormone therapy. Only elevated levels of conjugated oestrogens have been found to increase the relative risk although sufficient data is not available for an analysis of long-term effects. Combination therapy was reported to have a protective effect in one study but the results have never been reproduced. Other studies have found no significant increase in the risk of breast cancer. Long-term results in subjects on progesterone replacement have not revealed any protector effect. Animal models have shown that progesterone opposes the proliferative effect of oestrogens on mammary tissue and would suggest that progesterone has a protective action. Most in vitro studies on human mammary tissue suggest that progesterone has an antioestrogenic effect on epithelial tissues. The epidemiological data available leads to the conclusion that the therapeutic regimen recommendations currently put forward remain valid. Further large long-term prospective randomized trials are needed to definitely answer the remaining questions.