PDCD1 and esophageal squamous cell carcinoma: More recently, trials of drugs targeting the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) pathway have demonstrated prolonged survival with anti-PD-1 antibodies versus chemotherapy in patients with advanced or metastatic ESCC whose disease progressed after first-line systemic therapy [7–9].