Selective Estrogen Receptor Modulators and Aromatase Inhibitors for Breast Cancer Chemoprevention

In premenopausal women, tamoxifen for 5 years reduces the risk of estrogen receptor (ER) -positive breast cancer for at least 10 years. Women <50 years of age experience fewer serious side effects. Vascular and vasomotor events do not persist after treatment regardless of age. Raloxifene use is consistently associated with a reduction in breast cancer risk. In postmenopausal women, raloxifene and tamoxifen reduce the risk of ER-positive invasive breast cancer with equal efficacy, but raloxifene is associated with a lower risk of thromboembolic disease, benign uterine conditions, and cataracts than tamoxifen in postmenopausal women. No evidence exists establishing whether a reduction in breast cancer risk from either agent translates into reduced breast cancer mortality. Overall quality of life is similar with raloxifene or tamoxifen, but the incidence of dyspareunia, weight gain, and musculoskeletal complaints is higher with raloxifene use, whereas vasomotor symptoms, bladder incontinence, gynecologic symptoms, and leg cramps were higher with tamoxifen use. Ongoing randomized, placebo-controlled trials investigating the use of third-generation aromatase inhibitors in the chemoprevention of breast cancer in postmenopausal women include the NCIC Clinical Trials Group MAP3 (ExCel) Trial (Exemestane in Preventing Cancer in Postmenopausal Women at Increased Risk of Developing Breast Cancer), and the IBIS-II trial.71 The North American MAP3 study randomized patients to exemestane or placebo in patients who refuse treatment with a SERM, and the international IBIS-II trial compares anastrozole for 5 years versus placebo for chemoprevention in patients at increased risk.