Hormone replacement therapy and breast cancer

Numerous studies on oestrogen replacement therapy have failed to incriminate the use of exogenous oestrogen as a cause of breast cancer in post-menopausal women. Since so many variables influence breast cancer risk, it has not been possible for any single study to evaluate every potential risk factor included in the epidemiological and clinical reports on hormone use and carcinoma of the breast. The relative risk (RR) for breast cancer in oestrogen users has been found to vary from 0.4 to 3.4, with the vast majority of investigators reporting an RR very close to 1.0, or no increased risk at all. There is growing evidence that progesterone deficiency may increase the risk for breast cancer in some women. At least three studies have indicated that the addition of progestogen to oestrogen replacement therapy may significantly decrease the risk for carcinoma of the breast. It was observed that the RR of breast cancer varied from 0.47 to 0.89 in these studies when oestrogen-progestogen users were compared with unopposed oestrogen users. However, it is pointed out that progestogens are not added to oestrogen replacement therapy to negate an increased risk of breast cancer from unopposed oestrogens, since oestrogen therapy does not increase the risk. Combination oestrogen-progestogen therapy is recommended for hormone replacement treatment, even in women who have had a hysterectomy, because it will reduce the risk for breast cancer in some women.