Effectiveness of radiation therapy for older women with early breast cancer.

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 < .001, log-rank test). Radiation therapy was most likely to benefit those aged 70-79 years without comorbidity (number needed to treat [NNT] to prevent one event = 21 to 22 patients) and was least likely to benefit those aged 80 years or older with moderate to severe comorbidity (NNT = 61 to 125 patients).
Conclusion: For older women with early breast cancer, radiation therapy was associated with a lower risk of a second ipsilateral breast cancer and subsequent mastectomy. Patients aged 70-79 years with minimal comorbidity were the most likely to benefit, and older patients with substantial comorbidity were least likely to benefit.