Merck & Co. reported post-marketing bridging studies confirming that two commercially available companion diagnostics reliably identify patients eligible for pembrolizumab in dMMR/MSI-H solid tumors. The work, published in BMC Cancer, addresses a core requirement for tumor-agnostic approvals: ensuring that the diagnostic assays used in routine practice match the evidence base generated with trial-specific clinical trial assays. The study details how diagnostics—based on immunohistochemistry for mismatch repair protein presence and PCR or next-generation sequencing for microsatellite instability—were compared to confirm concordance for patient classification. For precision oncology stakeholders, the bridging results strengthen the operational foundation for CDx-driven expansion beyond a single trial assay.