De-escalation of axillary surgery in breast cancer patients with 1-2 positive sentinel nodes after neoadjuvant systemic therapy.

e12612 Background: Axillary lymph node dissection (ALND) is the standard treatment for patients with tumor-positive sentinel nodes after neoadjuvant systemic therapy (NST). While the ACOSOG Z0011 trial demonstrated that sentinel lymph node biopsy (SLNB) alone was non-inferior to ALND in patients with limited nodal disease undergoing upfront surgery, its safety and efficacy in NST settings remain unclear, particularly for clinically node-positive patients. This study aimed to evaluate the feasibility of de-escalating axillary surgery by comparing the oncologic outcomes of SLNB alone versus ALND in breast cancer patients with 1-2 positive sentinel nodes after NST. Methods: This retrospective study included patients with cT1-4N0-2M0 invasive breast cancer treated with NST (2015–2022) at Seoul National University Hospital. Patients had 1-2 tumor-positive sentinel nodes and underwent either SLNB alone or ALND after SLNB. Those with direct ALND without SLNB were excluded. Clinical and pathological characteristics, event-free survival (EFS), distant metastasis-free survival (DMFS), and overall survival (OS) were compared between groups. Results: Among 408 patients, 79 (19.3%) underwent SLNB alone, and 329 (80.7%) underwent ALND. The median age was 49.0 years, with a follow-up of 51.8 months. In the ALND group, 155 patients (47.1%) received lumpectomy, while in the SLNB alone group, 44 patients (55.7%) underwent lumpectomy. Postoperative radiation therapy was administered to 98.2% of patients. Clinical T stage and tumor subtype distributions were similar, but the ALND group had more clinical N2 patients (45.3% vs. 29.1%, p = 0.022). Pathologic N staging in the ALND group revealed pN1 in 83.3% and pN2 in 16.7%. There were no significant differences in EFS (HR = 0.46, 95% CI: 0.18–1.17, p = 0.11), DMFS (HR = 0.42, 95% CI: 0.15–1.20, p = 0.10), or OS (HR = 0.49, 95% CI: 0.06–3.90, p = 0.50) in the SLNB alone group compared to the ALND group. Conclusions: SLNB alone, followed by appropriate adjuvant therapy, may be a feasible alternative to ALND in patients with 1-2 positive sentinel nodes after NST, reducing morbidity without compromising oncologic outcomes. Further prospective studies are warranted to confirm these findings.