Clinical Significance of Extranodal Extension in Mastectomy Patients with Limited Sentinel Lymph Node Macrometastases: A Contemporary Analysis

Purpose The clinical significance of extranodal extension (ENE) in patients with one to two macrometastatic sentinel lymph nodes (SLNs) remains controversial in the era of axillary de-escalation. This study evaluated the association between SLN ENE and axillary nodal burden in early breast cancer, specifically addressing the mastectomy population. Methods This retrospective cohort study included early-stage breast cancer patients with one to two macrometastatic SLNs who underwent SLN biopsy followed by axillary lymph node dissection (ALND). Continuous variables were summarized as median (interquartile range) and compared using non-parametric tests. Categorical variables were analyzed using chi-square or Fisher's exact tests. Logistic regression identified factors associated with SLN ENE and predictors of non-SLN metastasis. Results Among 191 patients (all mastectomy), 53 (27.7%) had ENE at the SLN. ENE-positive patients had significantly higher nodal burden than ENE-negative patients (median [IQR]: 1 [0–2.5] vs 0 [0–1]; p < 0.001). Post-ALND ENE was more frequent in the ENE-positive group (22.6% vs 5.8%; p < 0.001). No significant difference in non-SLN metastasis was observed between ENE size groups (50.0% vs. 68.0%; OR 2.13, 95% CI 0.75–6.08; p = 0.265), despite a trend toward higher nodal burden in the ENE > 2 mm group (p = 0.071). ENE independently predicted non-SLN metastasis (aOR 2.94, 95% CI 1.50–5.76; p = 0.002). Conclusion ENE at the SLN independently predicts non-SLN metastasis in mastectomy patients with limited SLN involvement. ENE size alone did not significantly predict non-SLN metastasis (p = 0.265) or axillary nodal burden (p = 0.071), suggesting that ENE presence or absence is the more clinically relevant metric.