Estrogen replacement therapy in breast cancer survivors

Abstract

To the Editor. —Dr Cobleigh and colleagues 1 state that the 27 studies they analyzed not consistently demonstrate an increased risk of breast cancer among women who have ever used ERT [estrogen replacement therapy]. However, they fail to recognize that most negative studies do not have sufficient power to rule out clinically significant differences (see confidence intervals in Table 1 of Cobleigh et al). Since the most reliable estimates of association of any factor with a disease are obtained from prospective cohort studies rather than retrospective case-control studies, it is important that a prospective analysis based on the Nurses' Health Study 2 showed a moderate increase in the risk of breast cancer associated with current use of ERT. Bergkvist et al 3 also found an increased risk of breast cancer in their prospective study from Sweden, which, in addition, showed no protection from the addition of progestins. Cobleigh et