De-escalation of Axillary Surgery in Early Breast Cancer: Translating SOUND and INSEMA into Clinical Practice

Objective: – To prospectively evaluate how often axillary staging can successfully be omitted in postmenopausal HR+/HER2- patients. Background: – Three randomized trials showed no difference in recurrence or survival outcomes with omission of sentinel lymph node biopsy (SLNB) in cT1-T2N0 patients with a negative axillary ultrasound (AUS) undergoing breast-conserving surgery (BCS). We prospectively evaluated applicability of this approach. Methods: – From 3/1/24 to 9/1/25, SLNB was omitted in postmenopausal women age 50–70 years with unicentric or multifocal, clinical stage 1, grade 1/2, HR+/HER2- cancers and a normal AUS undergoing BCS. After the results of INSEMA were reported, tumors up to 2.5 cm were included. Patients with pathology showing grade 3, T≥3 cm, or HR- or HER2+ underwent multidisciplinary discussion regarding the need for SLNB. Results: – In 437 patients with 442 cancers, the median patient age was 63 years, median mammographic tumor size was 0.9 cm, and 74% were grade 2. A total of 34 patients (8%) had high-risk features on final pathology (grade 3, n=20; T≥3 cm, n=11; HER2+, n=3) and 14 (3.2%) had SLNB. Of these, 2 had SLN metastases. A total of 96% of patients received radiotherapy (40% whole breast, 56% partial breast), 415 (95%) received adjuvant endocrine therapy, and 31 (7%) received chemotherapy. At 7.7-month median follow-up, there have been no axillary recurrences. Conclusion: – Adoption of the SOUND, INSEMA, and BOOG 13-08 data allowed omission of SLNB in 97% of postmenopausal patients age ≤70 years with cT1-2N0, grade 1/2, HR+/HER2- cancers and a normal AUS, reducing the burden of treatment.