Significance of Multi-Cancer Genome Profiling Testing for Breast Cancer: A Retrospective Analysis of 3326 Cases from Japan's National Database

Background: Breast cancer (BC) has the highest morbidity rate and the second-highest mortality rate of all cancers among women. Recently, multi-cancer genome profiling (multi-CGP) tests have become clinically available. In this study, we aimed to clarify the significance of multi-CGP testing of BC by using the large clinical dataset from The Center for Cancer Genomics and Advanced Therapeutics (C-CAT) profiling database in Japan. Materials and Methods: A total of 3744 BC cases were extracted from the C-CAT database, which enrolled 60,250 patients between June 2019 and October 2023. Of the 3744 BC cases, a total of 3326 cases for which the C-CAT included information on ER, PR, and HER2 status were classified into four subtypes, including TNBC, HR+/HER2-, HR+/HER2+, and HR-/HER2+. Comparisons between groups were performed by the chi 2 test or Fisher's exact test using EZR. Kaplan-Meier curves were created using the log-rank test. Results: Of all 3326 cases analyzed, 1114 (33.5%) were TNBC cases, HR+/HER2- accounted for 1787 cases (53.7%), HR+/HER2+ for 260 cases (7.8%), and HR-/HER2+ for 165 cases (5.0%). Genetic abnormalities were most frequently detected in TP53 (58.0%), PIK3CA (35.5%), MYC (18.7%), FGF19 (15.5%), and GATA3 (15.1%) across all BCs. The rate of TMB-High was 12.3%, and the rate of MSI-High was 0.3%, in all BC cases. Therapeutic drugs were proposed for patients with mutations in six genes: PIK3CA, ERBB2, PTEN, FGFR1, ESR1, and AKT1. The prognoses of HR+/HER2- cases were significantly (p = 0.044) better in the treated group than in the untreated group. Conclusions: These findings suggest that cancer gene panel testing is useful for HR+/HER2- cases.