PDCD1 and melanoma: Additional subgroup analyses restricting the melanoma cohort to homogeneous class of ICIs revealed that the prediction was significant for patients with melanoma undergoing treatment with PD-1 inhibitors (HR, 0.35, 95% CI, 0.21–0.61, p < 0.001), but not CTLA-4 inhibitors (HR, 0.89, 95% CI, 0.49–1.61, p = 0.706) (Additional file 1: Figure S1).