In our study, we demonstrated the existence of dMMR/MSI-H sinonasal tumors by testing MMR protein expression in multitumor TMA and in corresponding whole slide tumor staining of 174 tumor samples, including the most common tumor types of this area: SNSCC, adenocarcinoma, SNEC, SNUC and SPs. This evidence concerns the gene MRC1 and adenocarcinoma.