The FDA approved Foundation Medicine CDx assays for use as companion diagnostics with Pfizer’s Talzenna plus Xtandi in patients with homologous recombination repair (HRR) gene-mutated metastatic castration-resistant prostate cancer. The approval positions FoundationOne CDx within a specific treatment-selection framework for HRR alterations. For developers and payers, CDx approvals can expand the eligible patient pool while also reinforcing the clinical utility of genomic stratification in late-stage prostate cancer. The decision follows a broader regulatory pattern of strengthening the linkage between biomarker testing and targeted therapy combinations.