CD274 and esophageal squamous cell carcinoma: The European Medicines Agency approved programmed death 1 (PD-1) inhibitors plus chemotherapy as a first-line treatment for high PD-1-expressing ESCC.<h4>Methods</h4>We systematically searched randomized controlled trials of PD-1 or PD-L1 inhibitors as first-line treatment from PubMed, Embase, and Cochrane Library.