Abstract PS2-02-06: Benefit of adjuvant chemotherapy for early-stage hormone receptor positive and HER2 negative lobular breast cancer patients: Analysis based on genomic risk scores

Abstract Background: Invasive lobular carcinoma (ILC) accounts for 10-15% of breast cancer (BC) cases and is predominantly hormone receptor-positive (HR+) and HER2-negative (HER2-). Although existing data indicates that ILC is less responsive to chemotherapy (CT) than invasive ductal carcinomas, the benefit of adjuvant CT in early-stage (ES) ILC is incompletely characterized. Further, the utility of the Oncotype DX Recurrence Score (RS), which has been used to predict response to CT in HR+/HER2- BC, has been debated for ILC. To address these issues, we studied the role of adjuvant CT on overall survival (OS) and by RS categories in ES ILC. Methodology: We queried the National Cancer Database for patients (pts) with ES HR+ HER2- ILC who underwent upfront surgical resection between 2010-2021. Pts were categorized to two cohorts based on receipt of adjuvant CT (CT+ and CT-). Subgroup analyses were performed based on RS score categories: low (L) 0-15, intermediate (I) 16-25, high (H) ≥26). Kaplan-Meier curves and log-rank tests determined OS between cohorts. Multivariate Cox proportional hazards models assessed OS, adjusting for potential confounders including age, race, stage, grade, and treatment variables. Results: Of the 162,430 ILC pts identified, 79.6% received adjuvant CT. The CT+ cohort were more likely to be younger pts (median age, IQR: 65 (55, 75) vs 66 (56, 72) years), have fewer comorbidities (Charlson-Deyo score (CDS) 0: 82.5 vs 82.3%, CDS 1: 13.1 vs 12.6%), intermediate grade disease (64.1 vs 62.2%), tumors