High baseline expression of IFN-γ in PBMCs, in advanced melanoma patients responding to anti-PD-1 therapy may indicate that the immune system of these patients is already set to attack cancer cells (inflammatory or anti-tumoral mood) and, probably, the concomitant inhibition of anti-PD-1 is the “spark that lights the fire”, removing the brake that inhibits effector T cells against tumor. This evidence concerns the gene IFNG and cancer.