Impact of Residual Nodal Disease Burden on Technical Outcomes of Sentinel Lymph Node Biopsy for Node-Positive (cN1) Breast Cancer Patients Treated with Neoadjuvant Chemotherapy.

Background: Recent trials have demonstrated the feasibility of sentinel lymph node biopsy (SLNB) for cN1 breast cancer patients after neoadjuvant chemotherapy (NAC). This study evaluated the technical outcomes of SLNB by residual nodal disease volume.

Methods: From a prospective database, cT1-3 cN1 patients receiving NAC and surgery from 2016 to 2017 were identified. Performance measures of post-NAC physical exam and imaging-based axillary assessment were compared. For the patients who converted to cN0 and underwent SLNB, adequate mapping (defined as ≥ 3 SLN) and the false-negative rate (FNR) of intraoperative SLN evaluation were assessed by residual nodal disease volume (ypN1-3 vs ypN0[i+]/ypN1mi vs ypN0).

Results: Of 156 cT1-3 cN1 patients, 96 converted to cN0 and underwent SLNB. Adequate mapping was achieved for 64 patients (66.7%) and was not associated with nodal volume (p = 0.12). The FNR of the intraoperative SLN evaluation was 37.8%, and smaller nodal volume was associated with FNR (p < 0.01). Of 36 patients (37.5%) who achieved an axillary pathologic complete response, 24 (66.7%) had three or more negative SLNs and were safely spared axillary lymph node dissection (ALND). The positive predictive values of physical exam versus imaging-based post-NAC nodal assessment were respectively 88% and 69.8%.

Conclusions: This study showed SLNB to be an effective tool for minimizing axillary surgery in cN1 patients treated with NAC. However, important technical limitations exist, such as inability to identify three SLNs in more than two-thirds of patients and high-false negative rates for intraoperative SLN evaluation, particularly for patients with small residual nodal volumes. Preoperative counseling should include realistic assessment of the potential need for ALND in this population.