PDCD1 and esophageal squamous cell carcinoma: Among the total, only five phase 3 RCTs that investigated a PD-1 inhibitor plus chemotherapy versus chemotherapy as first-line therapy for advanced ESCC were identified: JUPITER-06 (13), RATIONALE-306 (14), ESCORT-1st (15), CheckMate 648 (16), and KEYNOTE-590 (17) (Table 2).