PDCD1 and metastatic melanoma: Nivolumab was the first anti-PD-1 blocking antibody that was approved for treatment of inoperable or metastatic melanoma based on the CheckMate 037 (NCT01721746) clinical trial.15 The trial demonstrated that a greater proportion of advanced melanoma patients achieved an objective response and fewer toxic effects compared to the alternative chemotherapeutic regimen.15 Since then, other anti-PD-1 therapies such as pembrolizumab, cemiplimab, and dostarlimab have also been approved.2 Targeting PD-L1 is also a viable approach to block the PD-1/PD-L1 inhibition pathway.