Analysis of DNA methylation and microRNA expression in NUT (nuclear protein in testis) midline carcinoma of the sinonasal tract: a clinicopathological, immunohistochemical and molecular genetic study

The aim of this study was a detailed clinicopathological investigation of sinonasal NUT midline carcinoma (NMC), including analysis of DNA methylation and microRNA (miRNA) expression. Three (5%) cases of NMC were detected among 56 sinonasal carcinomas using immunohistochemical screening and confirmed by fluorescence in situ hybridization. The series comprised 2 males and 1 female, aged 46, 60, and 65 years. Two tumors arose in the nasal cavity and one in the maxillary sinus. The neoplasms were staged pT1, pT3, and pT4a (all cN0M0). All patients were treated by radical resection with adjuvant radiotherapy. Two patients died 3 and 8 months after operation, but one patient (pT1 stage; R0 resection) experienced no evidence of disease at 108 months. Microscopically, all tumors consisted of infiltrating nests of polygonal cells with vesicular nuclei, prominent nucleoli and basophilic cytoplasm. Abrupt keratinization was present in only one case. Immunohistochemically, there was a diffuse expression of cytokeratin (CK) cocktail, CK7, p40, p63, and SMARCB1/INI1. All NMCs tested negative for EBV and HPV infection. Two NMCs showed methylation of RASSF1 gene. All other genes (APC, ATM, BRCA1, BRCA2, CADM1, CASP8, CD44, CDH13, CDKN1B, CDKN2A, CDKN2B, CHFR, DAPK1, ESR1, FHIT, GSTP1, HIC1, KLLN, MLH1a, MLH1b, RARB, TIMP3, and VHL) were unmethylated. All NMCs showed upregulation of miR-9 and downregulation of miR-99a and miR-145 and two cases featured also upregulation of miR-21, miR-143, and miR-484. In summary, we described three cases of sinonasal NMCs with novel findings on DNA methylation and miRNA expression, which might be important for new therapeutic strategies in the future.