Tamoxifen and contralateral breast cancer

Women with prior history of breast cancer have an approximately three times greater risk of developing cancer of the opposite breast than women with no such history. This risk may be even higher in certain subgroups, including patients with a family history of breast cancer and premenopausal women. The 1998 Oxford overview analysis demonstrated a highly significant reduction of 30% in the incidence of contralateral breast cancer (CBC) in patients treated with tamoxifen compared with those never treated with the drug. Additionally, longer durations of tamoxifen are associated with greater reductions in risk, such that 1 year, 2 years, and 5 years of treatment are associated with risk reductions of 13%, 26%, and 47%, respectively (Fig. 1). In contrast, a similar analysis of adjuvant chemotherapy trials in breast cancer demonstrated no such reduction in the incidence of CBC. In this review, we will examine the available data on tamoxifen and CBC and further attempt to characterize the secondary neoplasms.