Clinical trials showed a significant objective response rate in MCC patients, including durable remissions in virus-positive and virus-negative tumors.109 Pharmacodynamically, retifanlimab blocks PD-1 with high affinity, similar to other PD-1 inhibitors, and its safety profile is consistent with immune-related toxicities characteristic of checkpoint inhibitors110 (Table 1). This evidence concerns the gene PDCD1 and Merkel cell skin cancer.