In esophageal squamous cell carcinoma (ESCC), PD-L2 was shown to negatively associate with the number of PD-1+ tumor infiltrating lymphocytes (TILs), indicating that PD-L2 expressed on ESCC cells might restrain PD-1+ TILs activity, ultimately facilitating immune escape (39). This evidence concerns the gene PDCD1 and esophageal squamous cell carcinoma.