Real-World Implications of the SOUND Trial.

Background: The SOUND trial demonstrated that omission of sentinel lymph node biopsy (SLNB) is noninferior to axillary staging in patients with early-stage breast cancer (BC) and negative axillary ultrasound (AxUS). We examined the generalizability of these findings in patients with hormone receptor (HR)+HER2- disease.

Methods: Patients with cT1N0M0, HR+HER2- BC and negative AxUS undergoing breast conservation with SLNB from 2016 to 2023 were identified from a prospectively maintained database. Clinicopathologic characteristics, disease burden, adjuvant treatment, and oncologic outcomes were examined and compared with the SLNB arm of the SOUND trial. In postmenopausal patients, the impact of nodal status and 21-gene recurrence score on chemotherapy recommendations were also examined.

Results: Of 3972 patients with cT1N0M0 HR+HER2- breast cancer, 544 underwent AxUS; 312 met SOUND eligibility criteria. Median age was 57 (interquartile range [IQR] 48-64) years, and 199 (63.8%) were postmenopausal. Median (IQR) tumor size was 1.3 (0.9-1.7) cm, and 260 (83.3%) tumors were grade 1 or 2. Sentinel lymph node biopsy was positive in 38 (12.2%) patients. Only three (0.4%) had ≥ 4 positive lymph nodes. At a median follow-up of 26.2 (IQR 10.8-38.2) months, there were no axillary recurrences and one (0.3%) distant recurrence. Among postmenopausal women with recurrence score ≤ 25, chemotherapy recommendations were not associated with nodal status.

Conclusions: Examination of our real-world HR+ HER2- "SOUND-eligible" population suggests that nodal disease burden and oncologic outcomes are similar to the SOUND trial population, supporting careful implementation of trial results into multidisciplinary practice. In postmenopausal patients, omission of SLNB does not appear to impact adjuvant chemotherapy recommendations.