Abstract PS2-06-17: Olaparib Use and gBRCA Testing among HER2-Negative Early-Stage Breast Cancer Patients in the United States Community Oncology Setting

Abstract Background: Long-term follow-up of the OlympiA trial confirmed the efficacy and safety of olaparib among high-risk HER2-negative (HER2-) early breast cancer (eBC) patients with a germline BRCA (gBRCA) mutation. This retrospective study focused on olaparib users and aimed to describe the contemporary real-world landscape for HER2- patients in the community oncology setting with regard to biomarker testing, treatment patterns, and olaparib uptake. Methods: Electronic medical record data from The US Oncology Network were used for this retrospective study among adult HER2- eBC patients who initiated systemic adjuvant treatment between 01 Jan 2020 - 31 Oct 2024 (adjuvant treatment initiation date as index date). Patient selection was conducted in a stepwise method, prioritizing patients who initiated olaparib, followed by non-olaparib patients who received BRCA and genomic risk testing (ODX or Mammaprint), followed by non-olaparib patients with a high genomic risk score (defined as ODX≥25 or High Mammaprint result). Patient and treatment characteristics, including biomarker and testing patterns, were assessed descriptively. Results: There were 251 HER2- eBC patients considered eligible for the study (222 HR+, 27 TNBC, 2 HR untested). Overall, 216 (97.3%) HR+ patients had a high genomic risk score, 42 (16.7%) patients had a gBRCA mutation, and 34 (13.5%) initiated olaparib. The median (IQR) time from gBRCA result date to olaparib initiation date was 8.8 (1.0, 23.1) months. gBRCA testing rates varied by biomarker status, with 64.4% (n=143) of HR+ patients and 85.2% (n=23) of TNBC patients tested. Overall, 34% (n=85) of patients did not receive gBRCA testing, and 12% (n=19) of patients received gBRCA testing after adjuvant therapy initiation. Compared to the overall cohort, olaparib users were younger (46.7 vs. 55.3 years), were more likely to have a family history of cancer (91.2 vs. 81.7%), and had a higher proportion of TNBC patients (47.1 vs.10.8%). Conclusion: Despite utilizing patient selection methods that prioritized olaparib users as well as patients tested for BRCA and genomic risk, olaparib uptake in the real-world is limited among HER2- eBC patients. Eligibility for olaparib is dependent upon having a BRCA mutation, but findings show that one-third of patients, especially among HR+ patients, did not receive gBRCA testing. Current guidelines recommend gBRCA testing for all patients with breast cancer, and as a result, there is an opportunity to improve gBRCA testing rates and timing to identify additional patients who may be eligible for and benefit from targeted treatment such as olaparib. As olaparib uptake increases, ongoing research to describe clinical outcomes is recommended. Citation Format: K. Mishkin, M. Ru, M. Mabel Mardones, I. Sruti, J. Murphy, J. Guo, Q. Li, X. Xu, K. Hirschfield, J. A. Mejia, P. Conkling. Olaparib Use and gBRCA Testing among HER2-Negative Early-Stage Breast Cancer Patients in the United States Community Oncology Setting 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 PS2-06-17.