Survival Effects of Postmastectomy Adjuvant Radiation Therapy Using Biologically Equivalent Doses: A Clinical Perspective

Background: Postmastectomy radiation therapy reduces locoregional recurrence among women with operable breast cancer, but whether it improves survival has been controversial. We reanalyzed the results from 36 unconfounded trials (i.e., addition of radiation therapy was the sole discriminant between treatments being compared) that were identified in previous meta-analyses, which provided 38 comparisons. Methods: We used three predefined treatment categories for individual patient data: 1) a biologically equivalent dose (BED) of 40–60 Gy in 2-Gy fractions with an appropriate target volume, 2) an inadequate or excessive dose of radiation therapy, and 3) an inappropriate target volume. Effects of radiation therapy on 5-year and 10-year survival in each of the treatment categories were estimated from a cohort of 13 199 patients from the published rates or, if these were unavailable, from the published survival curves. We also used this categorization to reanalyze data from Early Breast Cancer Trialists' Collaborative Group (EBCTCG) postmastectomy studies. At 10 years, 16 (84%) of the 19 comparisons in our study coincided with those reported by the EBCTCG. All statistical tests were two-sided. Results: Twenty-five of the 38 available comparisons had used optimal and complete radiotherapy (i.e., category 1). Of these 25 comparisons, 17 had 5-year data, and these data showed that adjuvant radiation therapy was associated with a 2.9% absolute increase in survival (odds ratio [OR] of death = 0.87, 95% confidence interval [CI] = 0.79 to 0.96; P = .006). Thirteen category 1 trials had data at 10 years, and these data showed that adjuvant radiation therapy was associated with a statistically significant 6.4% absolute increase in survival (OR of death = 0.78, 95% CI = 0.70 to 0.85; P