Background. Whether extracapsular extension (ECE) of tumor in the sentinel lymph node (SLN) is an indication for axillary lymph node dissection (ALND) in patients managed by American College of Surgeons Oncology Group Z0011 criteria is controversial. Here we examine the correlation between ECE in the SLN and disease burden in the axilla. Methods. Patients meeting Z0011 clinicopathologic criteria (pT1-2, cN0 with <3 positive SLNs) were selected from a prospectively maintained database (2006-2013). Chart review documented the presence and extent of ECE. Neoadjuvant chemotherapy patients were excluded. Comparisons were made by presence and extent (≥2 vs. >2 mm) of ECE. Results. Of 11,730 patients, 778 were pT1-2, cN0 with <3 positive SLNs without ECE, and 331 (2.8 %) had ECE. Of these, 180 had ≤2 mm and 151 had >2 mm of ECE. Patients with ECE were older (57 vs. 54 years; p = 0.001) and had larger (2.0 vs. 1.7 cm; p < 0.0001), multifocal (p = 0.006), hormone receptor-positive tumors (p = 0.0164) with lymphovascular invasion (p < 0.0001). Presence and extent of ECE were associated with greater axillary disease burden; 20 and 3 % of patients with and without ECE, respectively, had ≥4 additional positive nodes at completion ALND (p < 0.0001), and 33 % of patients with >2 mm ECE had ≥4 additional positive nodes at completion ALND, compared with 9 % in the <2 mm group (p < 0.0001). On multivariate analysis, >2 mm of ECE was the strongest predictor of ≥4 positive nodes at completion ALND (odds ratio 14.2). Conclusions. Presence and extent of ECE were significantly correlated with nodal tumor burden at completion ALND, thus suggesting that >2 mm of ECE may be an indication for ALND or radiotherapy when applying Z0011 criteria to patients with metastases in <3 SLNs. ECE reporting should be standardized to facilitate future studies.
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ACKNOWLEDGMENT This study was funded in part through NIH/NCI Cancer Center Support Grant No. P30CA008748 and the Cary Grossman Breast Fellowship Fund DISCLOSURES The authors have no conflicts of interest to declare.