MLH1 and squamous cell carcinoma: Using an immunohistochemical analysis of PMS2, MLH1, MSH2, and MSH6, Villanueva et al. [73] identified MSI in 2/25 SNUCs, 2/6 SNECs, and 0/14 ONBs, while in a large study of different sinonasal cancer types Hieggelke et al. [74] found MSI in only 4/125 squamous cell carcinomas but not in SNUCs or SNECs.