More recently, clinical trial data have demonstrated the utility of measuring microsatellite instability (MSI) status and/or DNA mismatch repair deficiency (dMMR) as predictive markers for response to PD-1 blockade independently from tumor cell of origin, resulting in the first FDA pan-cancer approval of a therapeutic in oncology (pembrolizumab) [6]. This evidence concerns the gene PDCD1 and neoplasm.