ABSTRACT: BACKGROUND:Pathologic complete response (pCR) after neoadjuvant chemotherapy (NACT) is associated with improved overall survival (OS) in patients with breast cancer, but it is unclear how post-NACT response influences radiation therapy administration in patients presenting with node-positive disease. We sought to determine whether nodal pCR is associated with likelihood of receiving nodal radiation and whether radiation therapy among patients experiencing nodal pCR is associated with improved OS. METHODS AND MATERIALS:Clinical N1 (cN1) female breast cancer patients diagnosed during 2010 to 2015 who were ypN0 (ie, nodal pCR; n = 12,341) or ypN1 (ie, residual disease; n = 13,668) after NACT were identified in the National Cancer Database. Multivariate logistic regression was used to identify factors associated with receiving radiation therapy. Cox proportional hazards modeling was used to estimate the association between radiation therapy and adjusted OS. RESULTS:The study included 26,009 patients; 43.9% (n = 5423) of ypN0 and 55.3% (n = 7556) of ypN1 patients received nodal radiation. Rates of nodal radiation remained the same over time among ypN0 patients (trend test, P = .29) but increased among ypN1 patients from 49% in 2010 to 59% in 2015 (trend test, P < .001). After adjusting for covariates, nodal pCR (vs no stage change) was associated with decreased likelihood of nodal radiation after mastectomy (?20% decrease) and lumpectomy (?30% decrease; both P < .01). After mastectomy, nodal (vs no) radiation conferred no significant survival benefit in ypN0 patients, but it approached significance for ypN1 patients (hazard ratio [HR], 0.83; 95% confidence interval [CI], 0.69-0.99, P = .04; overall P = .11). After lumpectomy, nodal radiation was associated with improved adjusted OS for ypN0 (HR, 0.38; 95% CI, 0.22-0.66) and ypN1 patients (HR, 0.44; 95% CI, 0.30-0.66; both P < .001), but this improvement was not significantly greater than that associated with breast-only radiation. CONCLUSIONS:ypN0 patients were less likely to receive nodal radiation than ypN1 patients were, suggesting that selective omission already occurs and, in the context of limited survival data, could potentially be appropriate for select patients.
