Abstract PS2-01-14: Omission of sentinel lymph node biopsy among women age 50-70: applying updated ASCO guidelines to a real-world population

Abstract Background: In April 2025 the American Society for Clinical Oncology (ASCO) published practice-changing guidelines recommending the omission of sentinel lymph node biopsy (SLNB) in patients with early-stage breast cancer over the age of 50. We aimed to evaluate factors associated with a positive SLNB and the impact on adjuvant therapy among patients meeting updated ASCO Guideline recommendations for SLNB omission. Methods: A single-institution retrospective cohort study of patients 50-70 years old diagnosed with early-stage invasive breast cancer (cT1N0, grade 1-2, ER+, HER2-) between 2022-2024 who underwent SLNB. All patients were cN0 and pre-operative axillary ultrasound (axUS) was not required. The primary outcome was SLNB positivity (SLNB+), defined as at least pN1mi, and secondary outcome was adjuvant treatment. Categorical covariates were compared in univariate analysis using Fischer’s exact test. Multivariable logistic regression was used to evaluate factors associated with SLNB+, adjusting for relevant clinical characteristics. Results: Among 282 patients meeting ASCO guideline criteria, 275 (97.5%) had SLNB results available for analysis. Among the cohort with SLNB, median age was 63 years (IQR 58-66) and the majority (81.0%) were ductal histology (Table 1). Adjuvant therapy included hormonal therapy (87.0%), whole breast radiation (73.0%), partial breast radiation (19.0%) and chemotherapy (5.8%). SLNB was positive in 17 (6.2%) patients (9 pN1mi, 8 pN1a, 0 pN2). Among those with pN1a, two patients had 2 positive nodes (one was pT2 and one had Oncotype Recurrence Score RS of 29) and no patients had 3 nodes. Factors associated with SLNB+ included tumor grade, pathologic tumor stage and Oncotype RS. In multivariable analysis, younger age and Oncotype RS were associated with SLNB+ but not tumor grade or tumor stage (Table 1). Among the 17 patients with SLNB+, 5 (29.4%) received chemotherapy of which 4 had a high Oncotype RS and 1 was pT2 on final pathology. Per 2024 Updated ASTRO Guideline, APBI would have been suitable for 8, and cautionary or not recommended for 6 patients with SLNB+ based on risk factors alone (3 pT2, 2 lobular histology, 1 with lymphovascular invasion LVI), and potentially 3 other patients with Oncotype RS 25. Among 8 patients with pN1a, 2 had a high-risk feature (both Ki6720%) indicating eligibility for adjuvant CDK4/6i per 2024 ASCO Guideline. Conclusion: In this cohort of 50- to 70-year-old patients with cT1N0 tumors meeting ASCO Guidelines for SLNB omission in the real-world setting of inconsistent pre-operative axUS, 6.2% were SLNB+. No decisions about chemotherapy would have been affected by the omission of SLNB. The positive SLNB could have impacted a total of 10 (3.6%) patients who may have received APBI instead of WBRT or not been eligible for CDK4/6i. Citation Format: E. C. Namoglu, A. Meisner, M. R. Flanagan, E. F. Gillespie. Omission of sentinel lymph node biopsy among women age 50-70: applying updated ASCO guidelines to a real-world population abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-01-14.