Sentinel Lymph Node Biopsy for Patients With cN1 HR+/HER2− Breast Cancer and Palpable Adenopathy

Importance: Randomized trials established the safety of omitting axillary lymph node dissection (ALND) among patients with clinically node-negative breast cancer and less than 3 positive sentinel lymph nodes (+SLNs) having upfront surgery and adjuvant radiation. Patients with palpable mobile level I/II axillary adenopathy (cN1) were not eligible for these studies. Presently, more than 80% of patients with HR+/HER2- cN1 disease undergo ALND either at upfront surgery or after neoadjuvant therapy, despite evidence that 50% to 60% will have only 1 or 2 positive nodes. Objective: To determine upfront sentinel lymph node biopsy (SLNB) feasibility and evaluate ALND rate among patients with HR+/HER2- cN1 breast cancer selected with axillary ultrasound (AUS). Design, Setting, and Participants: This nonrandomized clinical trial involved patients with cTx/cT1-2 cN1 HR+/HER2- breast cancer with 3 or fewer morphologically abnormal nodes on AUS at 4 centers. The trial began on April 20, 2021, and the database for this report was frozen on September 26, 2024. Interventions: Patients underwent upfront lumpectomy/mastectomy and SLNB, with single/dual-tracer mapping. ALND was indicated for 3 or more positive SLNs. Main Outcomes and Measures: The primary outcome was ALND rate. Secondary outcomes were frequency of palpable nodes being radioactive/blue and locoregional recurrence. Results: Among 78 enrolled patients, the median (IQR) age was 58 (49.0-66.5) years. Most tumors were cT1 (37 [47%]) or cT2 (40 [51%]), 56 patients (72%) had ductal histology, and 59 tumors (76%) were moderately differentiated. On AUS, 39 patients (50%) had 1 abnormal-appearing node, 33 (42%) had 2, and 6 (8%) had 3. Median (IQR) pathologic tumor size was 2.3 (1.6-3.3) cm, 50 patients (64%) had lymphovascular invasion, and 54 (69%) had extracapsular extension. SLNB was performed with dual tracer in 68 (87%), and 3 or more SLNs were retrieved in 75 (96%). The palpable diseased nodes were blue and/or radioactive in 107 of 161 instances (66.5%). Overall, 24 patients (31%) had 1 +SLN, 30 patients (38%) had 2 +SLNs, and 24 patients (31%) had 3 or more +SLNs. SLNB alone was performed in 59 patients (76%), while 19 (24%) had ALND; indicated ALND was deferred in 5 cases. Among those with 12 months or more follow-up (n = 68; median, 25 months), there have been no isolated axillary or locoregional recurrences. Conclusions and Relevance: This study found that SLNB is feasible among patients with cN1 HR+/HER2- disease and that resection of palpable nodes is necessary to minimize false-negative rates. This approach affords the opportunity to omit ALND and minimize morbidity among patients with cN1 cancer and limited nodal burden. Trial Registration: ClinicalTrials.gov Identifier: NCT04854005.