Effect of Postmastectomy Radiation on Survival of AJCC pN2/N3 Breast Cancer Patients.

BACKGROUND The effectiveness of postmastectomy radiation (PMRT) in breast cancer patients with N2 and N3 nodal status is often evaluated in combination with other postmastectomy adjuvant treatments. To account for interaction effects and determine the individual impact of PMRT alone, the National Cancer Data Base (NCDB) was analyzed from 2004-2011. PATIENTS AND METHODS We evaluated a cohort of 38,442 women diagnosed with pathological stage N2/N3 breast cancer who underwent mastectomy between 2004 and 2011 from the NCDB. Overall survival was the outcome variable; primary predictor variable was treatment (PMRT, adjuvant anti-hormonal therapy, and adjuvant chemotherapy). Additional variables addressed and adjusted for included: age, race, Charlson Comorbidity index, education, income, payer status, distance traveled, facility type, diagnosing/treating facility, treatment delay, grade of tumor, tumor size, and stage at diagnosis, tumor histology, ER/PR status, and lymph node invasion as well as PMRT boost and dosage. Multivariate Cox regression was used to investigate the effect of PMRT on overall survival while adjusting for secondary predictive factors. RESULTS The majority of patients received one or more postmastectomy procedures such as radiation (69.31%), chemotherapy (88.79%), and/or hormone therapy (62.66%). The median overall survival for all patients was 8.41 years. In multivariate analysis, effects of treatment on survival were significant for chemotherapy alone, hormonal therapy alone, and a combination of PMRT with either chemotherapy, hormonal therapy, or both. Compared to patients without treatment, patients who received PMRT alone were not significantly associated with an increased risk of death; patients who received hormone therapy alone or chemotherapy alone had a reduced risk of death by 15% and 31%, respectively. With the combination of all three treatments, risk of death was reduced by 64%. CONCLUSION PMRT was not found to be a significant predictor of risk of death for pN2/N3 breast cancer patients when adjusting for socioeconomic factors, disease characteristics, and interaction effects of chemotherapy and hormonal therapy. The benefit of PMRT in addition to chemotherapy, hormonal therapy or both on overall survival seems to be marginal and not statistically significant.