Abstract PO4-14-04: Comprehensive genomic profiling results in patients with metastatic breast cancer due to germline BRCA1/2 status and their HER2-low status

Abstract

Abstract Objective: To determine the usefulness of comprehensive genomic profiling testing and the percentage of HER2-low in patients with germline BRCA1/2 (gBRCA1/2) variants metastatic breast cancer. Methods: We included 3404 patients with metastatic recurrent breast cancer who underwent CGP testing from June 2019 to June 2023 in Japan. We examined the proportion of patients with or without recommended therapy, the proportion of patients who received matched therapy, and the proportion of patients with HER2 low by gBRCA1/2 variant due to CGP testing. RESULTS.: Of the 3404 patients, 69 (2.0%) had gBRCA1, 136 (4.0%) had gBRCA 2, 5 (0.1%) had gBRCA1 & gBRCA2, 1807 (53.1%) were negative, and 1388 (40.1%) were untested or unknown. The overall percentage of patients who recommended targeted therapy due to CGP testing was 37.4%(1272/3404), with gBRCA1 at 31.9%(22/69), gBRCA2 at 43.4%(59/136), and gBRCA1&gBRCA2 at 50%(2/4). The percentage of matched therapy performed in the 1st line after the expert panel was 8.3% overall, 2.9% for gBRCA1, 14.0% for gBRCA2, and 0% for gBRCA1&gBRCA2. The rate of tumor mutation burden (TMB) high was 7.4% overall, and gBRCA1 at 2 .9%, gBRCA2 at 9.6%, and gBRCA1&gBRCA2 at 50%. On the other hand, the percentage of HER2-low was 38.3% overall, 29% for gBRCA1, 58.1% for gBRCA2, and 25% for gBRCA1 & gBRCA2. Conclusion.: Germline BRCA2 variants had a higher rate of reaching matched therapy based on CGP test results. The higher rate of TMB high was suggested to be the reason for this. The high percentage of patients with HER2-low is also expected to improve the prognosis. Citation Format: Hiroshi Tada, Minoru Miyashita, Narumi Harada-Shoji, Yohei Hamanaka, Miku Sato, Mika Yanagaki, Satoko Tsunokake, Tokiwa Motonari, Tomomi Kon, Asumi Yamazaki, Takanori Ishida. Comprehensive genomic profiling results in patients with metastatic breast cancer due to germline BRCA1/2 status and their HER2-low status [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-14-04.