According to the subgroup analysis, we found that great heterogeneity in 1st line (p < 0.00001, I2 = 89%), anti-CTLA-4 (control group) (p = 0.008, I2 = 71%), melanoma (p < 0.00001, I2 = 89%), head and neck squamous cell carcinoma (p =0.05, I2 = 73%) groups. Here, CTLA4 is linked to head and neck squamous cell carcinoma.