Putative driver mutations in cancer-associated genes and genes of DNA repair of sinonasal cell lines. (a) Recurrently mutated cancer genes in the cell lines were listed in comparison to TCGA data of head and neck squamous cell cancer (HNSCC); genes belonging to the DNA repair system shaded in gray. Potential driver mutations were found in the TP53, EGFR, CDKN2A, CARD11 and KTN1 genes. Copy number loss (CNL) of BRCA2 and genes belonging to the homologous DNA repair (HR) as well as TP53 and CDKN2A were found in the cancer cell lines. Mismatch repair genes frequently carried gene variations, which were classified as benign according to ClinVAR database, except for the NC5′s MLH1 mutation, a somatic mutation with an allelic fraction of 99.8%, situated in the coding sequence for the ATPase region of MLH1 protein. (b) Immunohistochemical staining of MMR proteins revealed significant loss of MLH1 expression compared to the other cell lines (regular expression in NC1), followed by a complete loss of PMS2 protein expression but regular expression of MSH6 and MSH2. Scar bar 100 µm.