Abstract PS2-06-21: Real-word utilization of the 21-gene assay for guiding treatment decisions in patients with HR+/HER2- early breast cancer in the US

Abstract Objective: The 21-gene assay is both prognostic of distant recurrence and predictive of chemotherapy benefit and has been validated by evidence from randomized controlled trials in hormone receptor positive (HR+), human epidermal growth factor receptor-2 negative (HER2-) early-stage breast cancer (BC). This study explored real-world utilization of the 21-gene assay and subsequent treatment patterns in the US population. Methods: A retrospective study was conducted using de-identified data from Exact Science’s commercial database linked to STATinMED RWD Insights, an all-payer medical and pharmacy claims dataset. Female patients aged ≥18 years with ≥1 inpatient or ≥2 outpatient BC claims between January 1, 2015, and November 30, 2023, were included. First BC diagnosis was defined as the index date with patients required to have data 12 months pre- and 30 days post-index date. Patients were excluded if the index date occurred after the testing date, were pregnant, had another cancer diagnosis, or treated for cancer during the baseline period. Variables of interest included Recurrence Score® (RS) result and date, nodal, HR, and HER2 gene expression status and chemotherapy (CT) use (defined as any CT use within 12 months of index date). Descriptive analyses were conducted in the overall population by nodal status, by RS result category, and by race and ethnicity (Non-Hispanic Black (NHB), Non-Hispanic White (NHW), Asian, and Hispanic). Results: Among 119,383 early-stage HR+/HER2- BC patients in this analysis who underwent 21-gene assay testing, 21,706 (18.2%) had node-positive (N1), and 97,677 (81.8%) had node-negative (N0) disease. Among patients with N0 disease and available data in the specified groups, majority were NHW (56.5%), followed by Hispanic (9.0%), NHB (6.1%), and Asian (2.0%); a similar distribution was seen among patients with N1 disease. In the N0 cohort, most patients had low (0-10; 26.0%) or intermediate (11-25; 61.0%) RS results, while 12.9% had high (26-100) RS results. The distribution based on RS result was similar in the N1 cohort (86.1% low/intermediate risk (0-25), and 13.9% high risk (26-100)). The proportion of patients with a high RS result appeared numerically higher among NHB patients in both N0 (14.9%) and N1 (16.5%) compared with NHW (12.7%, 13.8%), Asian (12.5%, 14.3%), and Hispanic (12.9%, 14.2%) patients. Across both N0 and N1 disease, CT use increased with higher RS category overall and within each race and ethnic group. However, there were no apparent differences in CT use by race or ethnicity. Conclusions: This large real-world analysis of patients with early-stage HR+/HER2- BC shows that CT utilization increases appropriately with higher RS results, consistent with guideline-based care. Importantly, CT use was generally consistent across racial and ethnic groups, suggesting equitable application of RS-guided treatment recommendations. Citation Format: G. C. Carter, J. Racz, N. Gu, J. Bennett, Q. A. Le, M. Kohli, J. Rodriguez-Silva, Y. Barhoush, L. Batchu, Y. Abdou. Real-word utilization of the 21-gene assay for guiding treatment decisions in patients with HR+/HER2- early breast cancer in the US [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 PS2-06-21.