Differentiated Papillary NUT Carcinoma: An Unexpected, Deceptively Bland Presentation of a Sinonasal Carcinoma

Abstract

Abstract Background In recent years, the list of tumor entities in the sinonasal tract has significantly expanded, requiring advanced diagnostic testing. We report the case of a 32-year-old patient with an unusual NUT carcinoma originating in the maxillary sinus, which showed extensive well-differentiated, papillary squamous morphology, similar to the spectrum of the recently described DEK::AFF2 fusion-associated carcinoma. Methods We performed immunohistochemical and molecular studies including EBV- and HPV-testing, as well as DNA/RNA next generation sequencing. Results The tumor showed predominantly exophytic papillary growth with mature squamous differentiation. An additional component harbored atypical, less differentiated basaloid tumor cells with infiltration of the adjacent stroma. Conspicuous inflammation was evident. There was no evidence of HPV DNA or EBV RNA. Next-generation sequencing revealed a NUT::NSD3 gene fusion corresponding to (“speckled-type”) immunopositivity of NUT in the tumor cells. Conclusions We describe a NUT::NSD3 gene fusion-associated NUT carcinoma of the sinonasal tract with a deceptively well-differentiated papillary growth pattern, thus expanding the morphological spectrum of this typically poorly differentiated neoplasm.