Abstract PS5-03-12: Real-world BRCA and PD-L1 testing among first-line triple negative metastatic breast cancer patients

Abstract Background: Triple negative breast cancer is a less common, aggressive subtype that lacks the expression of estrogen and progesterone receptors as well as HER2, making standard endocrine and HER2-directed therapies ineffective. Current NCCN guidelines recommend germline BRCA testing for all patients (pts) with metastatic breast cancer to identify candidates for poly (ADP-ribose) polymerase (PARP) inhibitors. In addition, PD-L1 testing, defined as a combined positive score (CPS) ≥10, guides utilization of pembrolizumab in combination with chemotherapy. Taken together, biomarker testing is an important component in guiding care. The study describes patterns and timing of BRCA and PD-L1 testing among pts with mTNBC who initiated therapy. Methods: Pts with metastatic triple-negative breast cancer (mTNBC) who initiated therapy on or after January 1, 2021, were identified from the IntegraConnect PrecisionQ database, which includes electronic health records from over 3 million de-identified pts in the U.S. Metastatic status and biomarker information were verified through manual chart review, including extraction from unstructured clinical notes, genomic reports and pathology reports. The review captured hormone receptor and HER2 status, as well as documentation of BRCA and PD-L1 testing. Descriptive analyses compared testing rates by demographics, ECOG status, recurrent vs de novo presentation, and treatment patterns. Results: Overall, 720 curated pts were identified as having mTNBC and initiated a line of therapy on or after 1/1/2021 (date initiated minimum 1/1/2021; maximum 3/5/2025). Of the 720 pts, 651 (90%) received a BRCA genetic test, yet just 61% (n=437) were tested prior to the mTNBC therapy initiation date and among those 71% (N =311) received Germline testing. Out of the 651 pts who received a BRCA test, germline testing was recorded in 463 pts (71%), somatic testing in 536 pts (82%) and both types of tests were identified in 361 pts (55%). Prior to mTNBC therapy initiation, 42% (n=303) were tested for PD-L1 and 83% (N=600) were tested for PD-L1 at any time. The mean age for pts at treatment initiation date differed for those who received a BRCA test at any time compared to those who did not receive a BRCA test (mean age at treatment initiation date: BRCA tested 60 years old versus BRCA Not tested: 63 years old). Distribution of ECOG scores did not differ by PD-L1 or BRCA testing status at time of treatment of mTNBC. BRCA testing was similar across racial groups, but PD-L1 testing was lower in the African American population (68% vs. 76%). Out of all the PD-L1 CPS tested pts (N=384), a positive result, defined as a CPS that was ≥10, occurred in 49% (N=188) of cases and a negative result occurred in 51% (N=196) of cases. Among those who received a PD-L1 test after initiation of therapy, the median time to test was 29 days (interquartile range 10-151 days). Pts with recurrent disease had similar testing rates compared to those with de novo disease for both BRCA (89% vs. 91%) and PD-L1 (74% vs. 73%) testing. In the pts who tested positive for BRCA and negative for PD-L1 (n=36), PARP inhibitors were used in a subsequent line of therapy for 19 pts (53%). In the pts with a PD-L1 CPS ≥10 prior to mTNBC treatment initiation and did not receive pembrolizumab in the neo-adjuvant or adjuvant setting (n=166), pembrolizumab was utilized in 92 pts (55%). Conclusions: Out of all pts who were tested, only 42% of pts received PD-L1 testing and 61% received BRCA testing prior to initiating first-line treatment for mTNBC. Further opportunities for timely testing should be explored to optimize treatment choice. Citation Format: F. Kudrik, R. Choksi, D. Patt, S. Reddy, S. Reganti, S. Rosenfeld, S. W. Champaloux, A. Shrivastava, D. Parris, A. Rui, M. Gart, C. Wall, B. Wang, P. Varughese, J. Donegan, L. Morere, R. Geller, J. Scott, V. Gorantla. Real-world BRCA and PD-L1 testing among first-line triple negative metastatic breast cancer patients [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 PS5-03-12.