Compared with the adoption of PD-1 or PD-L1 inhibitor alone, the combination regimen (PD-1 or PD-L1 plus CTLA-4) significantly increased the risk of developing rash (OR = 2.39, 95% CI: [1.67, 3.42]; I2 = 54%, Z = 4.79, p < 0.00001; Figures 5(a)–5(c)). This evidence concerns the gene CTLA4 and exanthem.