Following neoadjuvant chemotherapy (NAC), the optimal strategies for postmastectomy radiotherapy (PMRT) and regional nodal irradiation (RNI) after breast-conserving surgery (BCS) are controversial. In this analysis, we evaluate the impact of these radiotherapy (RT) approaches for women with clinically node-positive breast cancer treated with NAC in the National Cancer Database (NCDB).

Women with cT1-3 cN1 M0 breast cancer treated with NAC were divided into four cohorts by surgery [Mastectomy (Mast) versus BCS] and post-chemotherapy pathologic nodal status (ypN0 versus ypN+). Overall survival (OS) was estimated using the Kaplan-Meier method and RT approaches were analyzed using the log-rank test, multivariate Cox models, and propensity score-matched analyses.

From 2003 to 2011, 15 315 cases were identified including 3040 Mast-ypN0, 7243 Mast-ypN+, 2070 BCS-ypN0, and 2962 BCS-ypN+ patients. On univariate analysis, PMRT was associated with improved OS for both Mast-ypN0 (P = 0.019) and Mast-ypN+ (P < 0.001) patients. On multivariate analyses adjusted for factors including age, comorbidity score, cT stage, in-breast pathologic complete response, axillary surgery, ypN stage, estrogen receptor status and hormone therapy, PMRT remained independently associated with improved OS among Mast-ypN0 [hazard ratio (HR) = 0.729, 95% confidence interval (CI) 0.566-0.939, P = 0.015] and Mast-ypN+ patients (HR = 0.772, 95% CI 0.689-0.866, P < 0.001). No differences in OS were observed with the addition of RNI to breast RT for BCS-ypN0 or BCS-ypN+ patients. Propensity score-matched analyses demonstrated identical patterns of significance. On subset analysis, OS was improved with PMRT in each pathologic nodal subgroup (ypN0, ypN1, and ypN2-3) (all P < 0.05).

In the largest reported analysis of RT for cN1 patients treated with NAC, PMRT was associated with improved OS for all pathologic nodal subgroups. No OS differences were observed with the addition of RNI to breast RT.