PDCD1 and cancer: In this context, the dual blockade of PD-1 and CTLA-4 is currently explored in many cancers such as melanoma, where this combination improves the response rate [170], and four independent phase I/II, II and III trials are under evaluation for the combination of PD-1 and CTLA-4 blockade in HNSCC (U111-1166-0687, NCT02823574, NCT02741570, NCT02551159).