Implications for sentinel lymph node biopsy (SLNB) omission in patients with early-stage node-negative HR+/HER2- breast cancer undergoing mastectomy.

Abstract

580 Background: The SOUND and INSEMA trials demonstrated non-inferiority of SLNB omission in HR+/HER2- early-stage breast cancer (BC) patients with negative axillary ultrasound (AUS) undergoing breast conserving therapy (BCT). However, it remains unclear if this approach may be applied to patients receiving mastectomy. We evaluated outcomes in a similar patient population receiving BCT versus mastectomy. Methods: Using an institutional database (2010-2023), we identified patients with cT1N0M0 HR+/HER2- unifocal invasive ductal carcinoma with negative AUS who underwent upfront BCT (breast conserving surgery + Radiation therapy [RT]) or mastectomy +/- RT. All patients underwent SLNB. Clinicopathologic and treatment characteristics were compared by surgery type as well as clinical outcomes. Results: Among 1,506 patients, median age was 59 years (IQR 51-67), and 80% were postmenopausal. BCT was performed in 78.2% (n=1,178) while 21.8% (n=328) underwent mastectomy. Patients who underwent mastectomy were more likely to be younger, premenopausal, with larger and higher grade tumors (Table). SLN positivity rate was 7.7% with no significant differences by surgery type (7.6% vs 8.2%, p=0.684). Only 4 (1.2%) and 2 (0.2%) patients had pN2 disease in the mastectomy and BCT cohorts, respectively. More patients undergoing mastectomy had axillary lymph node dissection compared to patients undergoing BCT (6.96% vs 0.3%, p<0.001). Among mastectomy patients, 10.1% received RT with higher rates in node-positive patients (52.9% vs 5.1%, p<0.0001). Similarly, chemotherapy use was higher among node-positive mastectomy patients (76.5% vs 22.5%, p=0.0001). Among SLN-positive postmenopausal patients with 21-gene recurrence score (RS) <25, chemotherapy use was 16.6% (2/12) after BCT and 0% (0/4) after mastectomy. When RS was >26, chemotherapy use was 60% (27/45) after BCT and 85.7% (12/14) after mastectomy. Median follow up was 25.3 months (IQR 13.2-58.9). There were 3 (0.2%) axillary recurrences with 2 recurrences after mastectomy (1 of whom received RT). There were 7 (0.46%) distant recurrences, with 2 following mastectomy. Conclusions: Among patients with cT1N0M0 HR+/HER2- invasive ductal carcinoma with negative AUS, positive SLNs were identified in 7.7% with only 0.46% having pN2 disease. Low axillary and distant recurrence rates were observed regardless of surgery type. However, given that nodal status impacts RT use among mastectomy patients, further research investigating omission of SLNB in this cohort is warranted. BCT (N, %) TM (N, %) p-value Age (median, IQR) 60.8 (53.2-67.8) 55.7 (46.9-64.9) <0.00001 Premenopausal 198 (16.8) 101 (30.8) <0.00001 Grade 3 146 (16.7) 66 (22.8) 0.035 cT stage 0.002 T1mic 14 (1.2) 12 (3.7) T1a 56 (4.8) 19 (5.8) T1b 376 (31.9) 80 (24.4) T1c 732 (62.1) 217 (66.1) pT size (median, IQR) 1.4 (0.9-4) 1.35 (0.8-2.1) 0.022