Predicting Non-sentinel Lymph Node Metastases in Patients with a Positive Sentinel Lymph Node After Neoadjuvant Chemotherapy

Background: The standard of care for breast cancer patients treated with neoadjuvant chemotherapy (NAC) who have a positive sentinel lymph node (+SLN) after NAC is completion axillary lymph node dissection (ALND). This study aimed to develop a nomogram to predict additional nodal disease in patients with +SLN after NAC. Methods: The study reviewed patients 18 years of age or older who had invasive breast cancer treated with NAC followed by SLN surgery with +SLN and ALND between 2006 and 2017 at the authors’ institution. Factors predictive of positive non-SLNs were analyzed using uni- and multivariable logistic regression. Results: The study identified 120 patients with +SLN after NAC and ALND. Of these patients, 30.8% were clinically node-negative (cN−), and 69.2% were clinically node-positive (cN+) before NAC. Tumor biology was human epidermal growth factor receptor 2-positive (HER2+) for 20%, hormone receptor-positive (HR+)/HER2− for 66.7%, and triple-negative breast cancer (TNBC) for 13.3% of the patients. Additional nodal disease was found on ALND for 63.3% of the patients. In the univariate analysis, the factors predictive of positive non-SLNs were biologic subtype (TNBC and HR+/HER2− vs HER2+; p < 0.001), higher grade (p = 0.047), higher pT category (p = 0.02), SLN extranodal extension (p = 0.03), larger SLN metastasis size (p < 0.001), and higher number of +SLNs (p = 0.02). The factors significant in the multivariable analysis included number of +SLNs, grade 3 vs grade 1 or 2, HER2+ versus HER2−, cN+ versus cN−, and larger SLN metastasis size. The resulting model showed excellent discrimination (area under the curve, 0.82; 95% confidence interval, 0.74–0.90) and good calibration (p = 0.54, Hosmer–Lemeshow). Conclusion: A clinical prediction model incorporating biologic subtype, grade, clinical node status, size of the largest SLN metastasis, and number of +SLNs can help physicians and patients estimate the likelihood of additional nodal disease and may be useful for guiding decision making regarding axillary management.