SENOPAUSE: Evaluation of an ASCO-Derived Clinical Proxy for Axillary Risk Stratification in a Retrospective Cohort

Background Sentinel lymph node biopsy (SLNB) omission is increasingly considered in carefully selected postmenopausal patients with low-risk, early-stage breast cancer. However, the prevalence of occult nodal disease and the extent to which nodal information alters adjuvant management remain key concerns in real-world implementation. Methods We conducted a retrospective, two-center observational study using an institutional REDCap database populated from the electronic medical record. Consecutive patients treated surgically between 2023 and 2024 were screened and a strict proxy of ASCO eligibility criteria for SLNB omission was applied (postmenopausal; HR-positive/HER2-negative; invasive ductal carcinoma; T0–T1; grade 1–2; no neoadjuvant therapy). The primary outcome was the prevalence of pN1 disease within the ASCO-eligible cohort. Secondary outcomes included adjuvant chemotherapy use, whole-breast radiotherapy (WBRT), and availability of genomic testing. Results Among 662 screened patients, 211 met all ASCO proxy eligibility criteria and comprised the primary analysis cohort. Occult nodal involvement was observed in 20/211 patients (9.5%, pN1). Adjuvant chemotherapy was administered in 10/211 patients (4.7%), while WBRT was delivered in 203/211 (95.7%). Genomic testing was available in 17/211 patients (8.1%) and was predominantly low-risk among those tested (13/17, 76%). Within the pN1 subgroup (n=20), chemotherapy was administered in 4/20 patients (20%), and genomic testing was available in 8/20 (40%). Conclusion In a real-world cohort meeting strict ASCO proxy criteria, approximately one in ten patients had occult pN1 disease, yet adjuvant chemotherapy use remained uncommon and WBRT was near-universal. These findings support the concept that, in highly selected low-risk luminal breast cancers, nodal status may have limited impact on adjuvant treatment escalation, reinforcing the importance of rigorous selection and shared decision-making when implementing SLNB omission. Microabstract The 2025 ASCO guideline supports omitting sentinel lymph node biopsy (SLNB) in selected postmenopausal women with small, grade 1–2, HR+/HER2− breast cancer, a negative preoperative axillary ultrasound, and breast-conserving therapy. In a strict ASCO-proxy cohort (n=211), occult pN1 occurred in 9.48%. Despite nodal positivity, chemotherapy was uncommon (4.74%) and whole-breast radiotherapy was near-universal (96.21%), suggesting that nodal status had limited impact on downstream adjuvant treatment escalation in this setting and supporting the real-world safety and feasibility of these recommendations, in line with the ongoing de-escalation of axillary surgery.