PDCD1 and metastatic melanoma: In metastatic NSCLC, Rizvi et al. [21] first reported that three TMB-high ICB responders had tumors harboring deleterious mutations in several DNA repair and replication genes, including POLD1, POLE, and MSH2. Analogously, in a metastatic melanoma cohort, Hugo et al. [25] noticed significant enrichment of mutations in the homologous recombination (HR) repair gene BRCA2 in PD-1 blockade responders compared to non-responders.