Tamoxifen and raloxifene have been approved for the primary prevention of breast cancer in high-risk women, but are associated with an increased risk of serious side effects. Few studies have characterized risk–benefit profiles for chemoprevention among women who initiate tamoxifen or raloxifene outside of a clinical trial setting. Use of raloxifene and tamoxifen for chemoprevention was self-reported in 2014 to 2016 by participants in The Sister Study, a prospective cohort of women with a sister who had been diagnosed with breast cancer. After exclusions, 432 current raloxifene users and 96 current tamoxifen users were matched to 4,307 and 953 nonusers, respectively, on age and year of cohort enrollment. Conditional logistic regression was used to evaluate characteristics associated with chemoprevention use. Risk–benefit profiles were examined using published indices that assess the level of evidence (none, moderate, strong) that the benefits of chemoprevention outweigh the risk of serious side effects. Among current chemoprevention users, 44% of tamoxifen users and 5% of raloxifene users had no evidence of a net benefit. In analyses of factors associated with chemoprevention use, having strong evidence of benefit was a significant predictor of raloxifene use, but not of tamoxifen use. In our sample of women with a first-degree family history of breast cancer, raloxifene was more commonly used for breast cancer prevention than tamoxifen. Most raloxifene users, but <60% of tamoxifen users, were likely to benefit. Use of risk–benefit tables can help women and their healthcare providers make an informed decision about breast cancer chemoprevention
