PDCD1 and esophageal squamous cell carcinoma: Only one PD-1 inhibitor is approved for the treatment of advanced nasopharyngeal carcinoma (NPC [toripalimab]), while a number of these antibodies are approved for advanced non-small cell lung cancer (NSCLC [pembrolizumab, nivolumab, and cemiplimab]) and esophageal squamous cell carcinoma (ESCC [pembrolizumab, nivolumab, and tislelizumab]).