Patterns of post-mastectomy radiation therapy in clinically node positive breast cancer patients with pathologically negative lymph nodes after neoadjuvant chemotherapy.

Background To analyze postmastectomy radiation therapy (PMRT) utilization and its association with overall survival (OS) in patients presenting with node positive breast cancer who are pathologically node negative (ypN0) after neoadjuvant chemotherapy (NAC). Materials and methods Using the National Cancer Data Base (NCDB), we identified patients diagnosed between 2004 and 2013 with clinical T1-4 node-positive non-metastatic breast cancer who received NAC and underwent mastectomy with pathologically negative lymph node sampling. Multivariable regression models identified factors associated with PMRT use. The Cox proportional hazards model was used to evaluate predictors of mortality. Results The study included 8,766 clinically node-positive patients who met the study criteria. PMRT was delivered to 61.5% of patients. Overall PMRT utilization rate increased over the study period from 54.4% in 2004 to 65.2% in 2011. Predictors of PMRT use included larger tumor size, increasing clinical N stage, higher grade disease, receipt of hormone therapy, and greater number of lymph nodes examined. Unadjusted 5-year OS was 84.1% in the PMRT group and 83.8% in the non-PMRT group (p=NS). PMRT was not significantly associated with survival on multivariable analysis (hazard ratio [HR] 0.87; 95% confidence interval [CI] 0.73-1.03). Conclusion The delivery of PMRT has increased over time in women presenting with clinically node positive breast cancer who convert to ypN0 after NAC. While we identified multiple independent socioeconomic and clinical predictors of both PMRT utilization and survival, PMRT itself was not significantly associated with survival.