Current status and issues regarding genetic medicine after cancer gene panel testing in Japanese patients with metastatic prostate cancer

The present study investigated the current status and issues regarding publicly reimbursed comprehensive genomic profiling (CGP) tests in Japan, as well as the implementation status of genetic counseling for cancer susceptibility genes identified by tumor-only sequencing in patients with prostate cancer. The data of 86 patients with metastatic prostate cancer who underwent CGP tests at a single institution between August 2019 and November 2024 were reviewed using either FoundationOne^® CDx (F1CDx; n=63) or FoundationOne^® Liquid CDx (F1LCDx; n=23) CGP tests. Of the 86 patients, 19 (22.1%) received genotype-matched therapy (GMT) under public health insurance (PHI) and 33 (38.4%) received subsequent systemic therapy (SST) because no GMT was identified or available under PHI or in clinical trials. Progression-free survival was significantly longer in the GMT/PHI group compared with the SST group (median, 6.5 vs. 3.5 months; P=0.006). Declines in serum prostate-specific antigen levels of ≥50% were more frequent in the GMT/PHI group [9/19 (47.3%)] than in the SST group [7/33 (21.2%)] (P=0.049). Of the 14 suspected carriers of deleterious germline alterations, 7 (50%) received genetic counseling; of which, 6/7 patients underwent confirmatory germline tests and 2 were diagnosed with hereditary breast and ovarian cancer. Cancer genetic medicine offers clinical benefits for patients with metastatic prostate cancer; however, most patients do not receive GMT after CGP testing. The implementation of genetic counseling for cancer susceptibility genes is thus insufficient and requires improvement.