The aim of this study was to evaluate the presence of CD8+ TILs, PD-L1 expression and the expression of MLH1, MSH2, MSH6 and PMS2 as surrogate markers of MSI, in a series of poorly differentiated sinonasal carcinomas who had received conventional treatments, as possible indicators for treatment with immunotherapy. This evidence concerns the gene CD274 and nasal cavity and paranasal sinus carcinoma.