Comparison of breast cancer risk in women with and without systemic lupus erythematosus in a Medicare population.

Studies have suggested a decreased breast cancer risk in women with systemic lupus erythematosus. However, these studies enrolled younger patients identified primarily from lupus clinics. We compared the 5-year incidence of breast cancer among women with and without a diagnosis of SLE in a large population-based study of Medicare beneficiaries. We used a 20 % sample to create a cohort of 3,670,138 women from 2006 Medicare claims data with and without SLE at baseline. The study had 80 % power to detect whether the 5-year breast cancer incidence in the SLE cohort was 13 % higher or lower than the non-SLE cohort. Of the 18,423 women with SLE, 21 % were African American and 53 % were ≥65 years. The absolute age-adjusted risk for breast cancer in women with SLE was 2.23 (95 % CI 1.94-2.55) and 2.14 (95 % CI 1.96-2.34) in controls per 100 women. The overall absolute age and race adjusted incidence rate was 1.04 (95 % CI 0.90-1.21). Among women with SLE from "Others" (Hispanic, Native American, and/or Asian), the age-adjusted risk for breast cancer was 2.44 per 100 women (95 % CI 1.07-2.18), and age-adjusted incidence rate was 1.52 (95 % CI 1.07-2.18). In contrast to prior clinic-based studies, this population-based cohort study showed that the risk of breast cancer in women with SLE was not lower than in women without SLE. Women with SLE should follow routine breast cancer screening recommendations for their age group to avoid delay in diagnosis, because the presence of SLE may affect selection of early breast cancer therapies.