The prognostic significance of low-volume residual nodal disease following neoadjuvant chemotherapy (NAC) is unknown.

Women with cT1-4N0-1 breast cancer treated with NAC were identified from Dana-Farber/Brigham and Women's Cancer Center (DFBWCC) and the National Cancer Database (NCDB). Disease-free survival (DFS) and overall survival (OS) estimates according to pathologic nodal status were calculated using the Kaplan-Meier method, with Cox proportional hazards regression used to assess the effect of clinical variables on survival outcomes.

Among 967 DFBWCC patients, 27 (2.8%) had residual isolated tumor cells (ITCs) and 61 (6.3%) had micrometastases. Five-year DFS was significantly worse in those with residual ITCs (73.5%) and micrometastases (74.7%) relative to those who were ypN0 following NAC (88.4%, p < 0.001). On adjusted analysis, those with residual ITCs (hazard ratio [HR] 2.4, 95% confidence interval [CI] 1.20-3.81) and micrometastases (HR 2.14, 95% CI 1.20-3.81) had increased risk of recurrence relative to ypN0 patients. Among 35,536 NCDB patients, 543 (1.5%) had ITCs and 1132 (3.2%) had micrometastases. Five-year OS estimates were significantly worse with increasing residual nodal burden: ypN0, 88.9%; ypN0[i+], 82.8%; ypN1mi, 79.5%; ypN1, 77.6% (p < 0.001). Compared with patients with ypN0 disease, NCDB patients with ITCs and micrometastases had 1.9- and 2.2-fold risk of death (p < 0.001). On subgroup analysis, the effect of low-volume residual disease on mortality was most pronounced in patients with triple-negative and human epidermal growth factor receptor 2 (HER2)-positive disease.

Low-volume residual nodal disease following NAC is associated with poorer DFS and OS relative to those who are node negative.