CD274 and esophageal squamous cell carcinoma: Tissue sections of ESCC were immunohistochemically stained with PD‐L1 antibody, and PD‐L1 expression was scored using the PD‐L1 IHC 22C3 CPS scoring method to divide patients into the PD‐L1‐positive and PD‐L1‐negative groups.