Mismatch repair deficiency signature in SNSCC cell line. (a) Mutational signature analysis based on WES of 6 patient-derived sinonasal squamous cell carcinoma (SNSCC) cell lines (NC) and one patient’s lymph node metastasis (NC6-LM)/tumor recurrence (NC6-relapse). A sinonasal intestinal type adenocarcinoma (ITAC3) revealed a mismatch repair-deficient signature of NC5 (signature 6, 15, 20, 26). NC6-primary, ITAC3, NC1, NC4 and NC8 clustered with the highest impact of age-associated signature (1). NC6-primary, ITAC3, NC1 and NC8 showed alteration resembling homologous recombination (HR) repair system deficient tumors (signature 3), which was the predominant signature of NC6-relapse, NC6-LM and NC7 (signature 3). NC9 mostly collected smoking-associated mutations (signature 4). (b) Tumor mutational burden (TMB) analysis of cell line samples revealed an average of variants per covered mega base (MB) of 13.67 for non-synonymous and for all coding sequencings of 17.784, confirming a TMB-high status for NC5. (c) Analysis of microsatellite sites in WES data of cell lines elucidated an abnormal percentage of instable microsatellite regions compared to all analyzed sites in individual normal tissue control, classifying the NC5 as a highly microsatellite instable (MSI-H) carcinoma.