PDCD1 and esophageal squamous cell carcinoma: All studies were open-label, phase 2 non-RCTs, and 25 of them were single-group21,22,24,25,26,27,30,31,33,34,35,36,37,39,40,41,42,43,44,45,46,47 and 2 were dual-group trials.28,29 Twenty-three trials21,23,24,27,28,29,31,32,33,34,35,36,37,38,39,42,43,44,46,47 enrolled patients with ESCC and applied anti–PD-1 antibody.