Implications for Sentinel Lymph Node Biopsy Omission in Patients with Early-Stage Node-Negative HR+/HER2- Breast Cancer Undergoing Mastectomy.

[INTRODUCTION] The SOUND and INSEMA trials have demonstrated the non-inferiority of sentinel lymph node (SLN) biopsy (SLNB) omission in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) early-stage breast cancer (BC) with negative axillary ultrasound undergoing breast-conserving therapy (BCT). We evaluated SLNB positivity rates and treatment characteristics among patients undergoing BCT versus mastectomy.

[METHODS] Patients with cT1N0M0 HR+/HER2- unifocal invasive ductal carcinoma with negative axillary ultrasound undergoing upfront BCT + radiation therapy (RT) or mastectomy +/- RT were included (2010-2023). Clinicopathologic characteristics, treatment, and patient outcomes were compared by surgery type.

[RESULTS] Among 1506 patients, the median age was 59 years (interquartile range [IQR] 51-67). In total, 78.2% (1178) underwent BCT and 21.8% (328) underwent mastectomy. The mastectomy cohort was significantly younger and had larger and higher-grade tumors (age 55.7 vs. 60.8; grade 3: 20.1 vs. 12.5%, both p < 0.001). Rates of positive SLNs were similar in BCT and mastectomy cohorts (7.6 vs. 8.2%, p = 0.684). Among the mastectomy cohort, 10.1% received RT and 28.1% received chemotherapy, with higher rates in patients with positive SLNs (RT: 51.8 vs. 6.31%, chemotherapy: 76.5 vs. 22.5%, both p < 0.0001). At a median follow up time of 25.3 months (IQR 13.2-58.9), three (0.2%) had axillary recurrences (two after mastectomy) and seven (0.46%) had distant recurrences (two after mastectomy).

[CONCLUSIONS] Among patients with cT1N0M0 HR+/HER2- disease and negative AUS who underwent SLNB, early recurrence rates were low regardless of surgery type. Given that nodal status affects the use of RT after mastectomy, further research investigating the omission of SLNB in this cohort is warranted.