Abstract 920: Real-world biomarker testing patterns in metastatic castration-resistant prostate cancer patients

Abstract Introduction: Homologous recombination repair mutations (HRRm) result in an accumulation of genetic aberrations and genomic instability. HRRm are estimated to be present in up to 28% of patients (pts) with advanced prostate cancer, including metastatic castration-resistant prostate cancer (mCRPC). Testing for HRRm may inform treatment choice in pts with mCRPC. The aim of the study was to assess HRRm testing rate and describe pts factors associated with testing in treated mCRPC pts. Methods: We identified pts with mCRPC on treatment from 5/1, 2020 through 3/31, 2022 from the Integra Connect PrecisionQ de-identified database, an electronic medical record (EMR) and claims database of US cancer pts in community oncology. We defined HRRm testing as the receipt of any test for alterations in 1 or more of the following genes: BRCA 1/2, ATM, BARD1, BRIP1, CDK12, CHEK1, CHEK2, FANCL, PALB2, RAD51B, RAD51C, RAD51D, RAD54. We described age and race at diagnosis (dx), cancer stage and Gleason score at staging, and line of therapy (LOT), Eastern Cooperative Oncology Group (ECOG) performance status, metastatic sites and prostate-specific antigen (PSA) values at date closest to mCRPC diagnosis. Categorical data were reported as counts and percentages, and continuous data were summarized as medians (IQR). Results: The study cohort comprised 798 pts (HRRm tested, n=389, 48.7%). Most pts were white (81.7%), with a median (IQR) age of 68 (54-82) years at dx. Most pts had high-grade mCRPC, with Gleason scores of 7-8 (43.3%) or 9-10 (47.9%). The majority of pts were stage IV (74.0%), and on their first LOT (44.6%) at mCRPC diagnosis. A higher proportion of pts ≥80 years were not HRRm-tested (61.5%) vs. pts ≤59 (46.6%). Compared to white pts, a higher proportion of black/African American pts were HRRm non-tested (48.6% vs 41.5%). Tested pts had better ECOG status compared to non-tested pts (0 - 1: 91.0% vs 86.8%). 77.1% of tested pts had a bone metastasis compared to 73.4% of non-tested. A higher proportion of tested pts were diagnosed with mCRPC in a later LOT than those not tested. Conclusion: We found a testing rate for HRRm of 49% in US mCRPC pts receiving routine care. There were modest unadjusted differences in demographic and clinical features between tested and non-tested pts. There is a need for further research to examine the value of HRRm testing in mCRPC pts. Citation Format: Simon Blanc, Gboyega Adeboyeje, Liam Lee, Mike Gart, William Saunders, Brandon Wang, Poras Dave, Sandy English, Prateesh Varughese, Arthur Sillah. Real-world biomarker testing patterns in metastatic castration-resistant prostate cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 920.