PDCD1 and digestive system neoplasm: Several molecules inhibiting the link between PD-1 and PD-L1 are currently used for the treatment of gastrointestinal tumors and specifically esophageal cancer: anti-PD-1 agents such as nivolumab and pembrolizumab, or anti-PD-L1-agents such as atezolizumab and avelumab [15].