PDCD1 and esophageal cancer: Clinically, there are two main immunotherapy options for patients with esophageal cancer, namely, anti‐programmed cell death 1 (anti‐PD‐1)/anti‐programmed cell death 1 ligand 1 (anti‐PD‐L1) and anti‐cytotoxic T‐lymphocyte‐associated antigen‐4 (anti‐CTLA‐4) therapy.8