Estrogen Replacement Therapy and Risk of Breast Cancer

To the Editor.— Colditz et al1from the Nurses' Health Study conclude that there is a statistically significant elevation of 36% in breast cancer risk that is limited to current users of estrogen replacement therapy, and that there is no relationship with duration of use. The report, however, does not consider an important risk factor for breast cancer: age at menopause. Although this is most unlikely to alter the conclusion about an elevation in breast cancer risk associated with use of estrogen replacement therapy, it raises serious doubts about the relationship's being restricted to current users and about there being no relationship with duration of use. It is generally accepted that earlier ages at menopause are associated with lower risks of breast cancer,2and we have found that women with early menopause have greater use of replacement hormones.3If use of estrogen replacement therapy is associated with