Breast Cancer Characteristics and Survival among Users versus Nonusers of Raloxifene

Raloxifene reduces breast cancer incidence. However, it is unclear whether it also reduces mortality from breast cancer. For raloxifene to reduce incidence but not mortality, breast cancer survival would have to be worse for raloxifene users than nonusers. Surveillance Epidemiology and End Results-Medicare was used to identify women with invasive breast cancer diagnosed from 2007 to 2015 at ages 65-89 who had prior Medicare Part D (prescription drug) enrollment; breast cancer characteristics and survival were assessed among raloxifene regular users (≥180 days in past year) versus nonusers. Logistic regression was used to assess cancer characteristics. Two methods utilizing proportional hazards models were employed to assess breast cancer-specific survival. In method 1, survival was assessed adjusting for demographics, mammography use, and chronic conditions in the subset with Medicare fee-for-service enrollment. In method 2, predicted survival as a function of breast cancer characteristics was modeled in nonusers and the model applied to users to predict survival. A total of 116,317 raloxifene nonusers and 1,223 regular users were identified. Users were significantly more likely to have hormone receptor (HR)-negative cancers, but less likely to have T2+, N1+, and metastatic disease. There were 10,869 and 101 breast cancer-related deaths in nonusers and regular users, respectively. The HR (users vs. nonusers) for breast cancer-specific survival in method 1 was 0.94 (95% confidence interval, 0.73-1.22). In method 2, predicted survival was higher in users than nonusers (8-year survival 84.9% vs. 83.4%). Breast cancer-specific survival in raloxifene users was not worse than in nonusers, providing indirect evidence that raloxifene reduces breast cancer-related mortality.