Background: Neoadjuvant chemotherapy (NAC) is known to downstage disease in the breast and increase breast conservation. It can also decrease nodal disease extent. We evaluated the impact of NAC on nodal positivity, nodal burden, and nodal surgery by tumor subtype. Methods: All cT1–4c breast cancers from 2010 to 2014 in the National Cancer Database were evaluated, comparing patients receiving NAC with those undergoing primary surgery (PS). Rates of pathologic node-negative status (pN0) and sentinel lymph node (SLN) surgery (1–5 nodes) were compared using chi-square tests, and adjusted odds ratios (OR) were estimated. Results: Of 461,549 patients, 36,715 (8.0%) received NAC and 424,834 (92.0%) had PS. In cN0 patients, pN0 rates were higher in NAC compared with PS patients in ER−/HER2+ [93.2 vs. 79.0%, odds ratio (OR) 3.64, p < 0.001], ER−/HER2− (89.9 vs. 85.2%, OR 1.55, p < 0.001), and ER+/HER2+ (84.7 vs. 78.3%, OR 1.54, p < 0.001). Patients with cT2–3, N0 tumors had significantly higher rate of SLN surgery for NAC versus PS for each biologic subtype except for ER+/HER2− tumors, amongst which this was true only for T3 tumors. In cN1–3 patients, pN0 rates after NAC were 61.3% in ER−/HER2+, 47.7% in ER+/HER2+, 47.3% in ER−/HER2−, and 20.2% in ER+/HER2− and SLN surgery was highest in ER−/HER2+ (28.9%, p < 0.05 versus other subtypes). Conclusion: NAC increases rates of pN0 among cN0 patients compared with PS. Among cN+ patients, 20–61% undergoing NAC convert to pN0 depending on tumor type, with lowest nodal response in ER+/HER2− disease. Use of NAC results in less extensive axillary surgery than in patients treated with PS in both cN0 and cN+ disease.
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