Effectiveness of radiation therapy for older women with early breast cancer

Abstract

Background: Recent clinical trials have questioned the necessity of breast radiation therapy for older women with early breast cancer. However, the effectiveness of radiation therapy for older women in the community setting has not been addressed. Methods: We used the Surveillance, Epidemiology, and End Results (SEER)-Medicare database from January 1, 1992, through December 31, 1999, to identify 8724 women aged 70 years or older treated with conservative surgery for small, lymph node-negative, estrogen receptor-positive (or unknown receptor status) breast cancer. We used a proportional hazards model to test whether radiation therapy was associated with a lower risk of a combined outcome, defined as a second ipsilateral breast cancer reported by SEER and/or a subsequent mastectomy reported by Medicare claims. All statistical tests were two-sided. Results: Radiation therapy, compared with no radiation therapy, was associated with a lower risk of the combined outcome (hazard ratio = 0.19, 95% confidence interval = 0.14 to 0.28). Radiation therapy was associated with an absolute risk reduction of 4.0 events per 100 women at 5 years (i.e., from 5.1 events without radiation therapy to 1.1 with radiation therapy) and 5.7 events per 100 persons at 8 years (i.e., from 8.0 events without radiation therapy to 2.3 with radiation therapy) (P