PDCD1 and esophageal squamous cell carcinoma: Among the 23 included ESCC studies that applied anti–PD-1 antibody, 8 used camrelizumab,32,35,36,39,43,44,46,47 4 used pembrolizumab,21,27,29,33 4 used sintilimab,23,27,40,41 4 used toripalimab,42 1 used tislelizumab,38 and 2 used multiple drugs.34,37 Due to the limitations of available data, exploratory subgroup analyses were conducted only in ESCC.