Breast Cancer Prevention with Selective Estrogen Receptor Modulators

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Abstract
Chemoprevention for breast cancer is both old and new. It has long been appreciated that early ovarian ablation dramatically reduces the incidence of breast cancer in premenopausal women. It was subsequently demonstrated, in the Early Breast Cancer Trialists' Collaborative Group (EBCTCG) overview, that tamoxifen results in a 40% or greater reduction in the incidence of contralateral breast cancer. Now, the National Surgical Adjuvant Breast and Bowel Project (NSABP) has shown a similar reduction in a randomized trial [Breast Cancer Prevention Trial (BCPT)] comparing tamoxifen and placebo in women aged 35 years or over at increased risk of developing breast cancer because of age, family history, or other factors. In this trial, the incidences of both ductal carcinoma in situ (DCIS) and invasive cancer were reduced. Reduction in incidence was similar over all years of the study and in all subgroups of high-risk women. However, all of the reduction was confined to estrogen receptor (ER)-positive tumors. Raloxifene, a newer selective estrogen receptor modulator (SERM) originally developed for osteoporosis, also appears to have a major preventive effect on breast cancer incidence. Limitations in the design and patient population of raloxifene trials, however, have made it difficult to as yet recommend raloxifene for risk reduction of breast cancer. The randomized Study of Tamoxifen and Raloxifene (STAR) study, which will compare raloxifene to tamoxifen in over 20,000 postmenopausal women at increased risk of breast cancer, as well as ongoing and proposed placebo-controlled studies of tamoxifen, the aromatase inhibitor anastrazole, and other antiestrogens in high- or average-risk postmenopausal women, will provide further results on optimal prevention strategies.