Hormone Replacement and Breast Cancer

Ever since replacement hormones were introduced some 30 years ago, there has been concern regarding a possible adverse effect on breast cancer risk. More than 30 epidemiological studies have explored the relationship between exogenous hormones and breast cancer. Most of them were of case-control design,¹⁻³while seven were prospective cohort studies.⁴⁻¹⁰Despite several attempts to summarize available evidence in overviews¹and through meta-analyses,²,³there is still considerable uncertainty as to whether replacement hormones increase breast cancer risk. However, some recent studies indicate that long-term intake of conjugated estrogens or estradiol compounds is associated with a moderate risk increase.⁶,⁸,¹¹⁻¹³The remaining controversy might be viewed as a shortcoming of the epidemiological method, ie, inability to clarify the role of a potential cause of breast cancer. According to a rival and more optimistic interpretation, the absence of unequivocal evidence for a risk-increasing effect of replacement hormones indicates