Merck reported post-marketing bridging study results confirming that two commercially available companion diagnostics can reliably identify patients eligible for pembrolizumab in dMMR/MSI-H solid tumors. Findings were published in BMC Cancer, addressing a core post-approval requirement that real-world CDx assays perform consistently with the original trial assay approaches. The analysis focused on how regulators assess diagnostic backbone transferability across immuno-oncology approvals, particularly for tumor-agnostic indications where biomarker detection—rather than tumor site—drives treatment eligibility. By validating bridging for the diagnostic tests used outside pivotal trials, the work reduces uncertainty for clinicians and testing networks implementing MSI/dMMR selection in routine practice.