Clinicopathological significance of NUT rearrangements in poorly differentiated malignant tumors of the upper respiratory tract.

Nuclear protein in testis (NUT) midline carcinoma (NMC) is a highly malignant carcinoma originating from the midline of the body. This study investigated the clinicopathological significance of NUT rearrangements in poorly differentiated malignant tumors (PDMTs) of the upper-respiratory tract (URT) in China. The clinical and pathological features of 155 PDMTs of the URT were reviewed. Epstein-Barr virus (EBV)-encoded RNA and NUT were investigated by in situ hybridization and immunohistochemistry (IHC), respectively. NUT-positive cases were examined by fluorescence in situ hybridization (FISH) and immunohistochemical staining with a set of cytokeratins (CKs) and neuroendocrine markers. One case was observed by transmission electron microscopy. Four cases of poorly differentiated squamous cell carcinomas and sinonasal undifferentiated carcinomas were diffuse positive for NUT by IHC and also stained for antibodies to CKs and P63 but were negative for neuroendocrine markers. Only 2 of these 4 cases showed rearrangements of the NUT and BRD4 genes by FISH; both these patients died within 12 months. The remaining 2 patients showed no NUT rearrangement by FISH and did not have an aggressive clinical course. NMC is a rare, poorly differentiated carcinoma, which occurs most often in midline organs, and in this first series from China, affected the sinonasal tract of older adults and was not associated with EBV infection. Determination of NUT protein expression and gene rearrangement can allow the differentiation of NMC from other URT PDMTs. The authors suggest that molecular determination of NUT gene rearrangements should therefore represent the gold standard for NMC diagnosis.