ICOS and head and neck squamous cell carcinoma: Besides PD-L1, PD-L2, PD-1, CD80, CD86, CTLA-4, Tim-3, LAG3, and 4-1BB, we found the increase of an inducible co-stimulator (ICOS) expression in both HPV-positive head and neck squamous cell carcinoma and EBV-positive stomach adenocarcinoma tumors.