PDCD1 and melanoma: Although tumor mutational burden (TMB) (8), the expression of programmed cell death protein ligand-1 (PD-L1) (9), tumor infiltrating lymphocytes (TILs) (10), and several melanoma/immune-pertinent signatures (11–14) have been reported to be positively correlated with a therapeutic benefit from anti-PD-1 monotherapy, these are tumor sample-based, thus, requiring invasive biopsy/surgical procedures and are also computationally demanding, which render them less feasible to be adopted in the daily clinical practice.