Postmastectomy Radiation in Breast Cancer Patients With Pathologically Positive Lymph Nodes After Neoadjuvant Chemotherapy: Usage Rates and Survival Trends

To analyze postmastectomy radiation therapy (PMRT) usage and its association with overall survival (OS) in breast cancer patients with pathologically positive lymph nodes after neoadjuvant chemotherapy (NAC).Using the National Cancer Database, we identified women with nonmetastatic breast cancer diagnosed from 2004 to 2013 who had received NAC and undergone mastectomy with macroscopic pathologically positive lymph nodes. Joinpoint regression models were used to assess temporal trends in annual PMRT usage. Multivariable regression models were used to identify factors associated with PMRT use. A time-dependent Cox model was used to evaluate the predictors of mortality.The study included 29,270 patients, of whom 62.5% received PMRT. PMRT was markedly underused among all nodal subgroups, in particular, among ypN2 (68.4%) and ypN3 (67.0%) patients. Hispanic patients and those with Medicaid or Medicare insurance were less likely to receive PMRT than were non-Hispanics and patients with other insurance carriers. The adjusted 5-year OS rates were similar in ypN1 and ypN2 patients with or without PMRT but were significantly greater in ypN3 patients receiving PMRT (66% vs 63%; P=.042). On multivariable analysis, PMRT was associated with improved survival only among ypN3 patients after adjusting for patient, facility, and tumor variables (multivariable hazard ratio 0.85; 95% confidence interval 0.74-0.97).A considerable portion of breast cancer patients with advanced residual nodal disease after NAC did not receive appropriate adjuvant radiation. We also found socioeconomic disparities in national PMRT practice patterns. Patients with ypN3 disease might derive a survival benefit from PMRT.