PDCD1 and esophageal squamous cell carcinoma: Secondly, in this systematic review and meta-analysis, a total of 1651 ESCC patients from 9 studies received anti-PD1 therapy (tislelizumab, toripalimab, pembrolizumab, camrelizumab, sintilimab, and nivolumab) and only 37 patients from 1 study received anti-PD-L1 therapy (CS1001).