NUT (Nuclear Protein in Testis) Carcinoma: A Report of Two Cases With Different Histopathologic Features.

NUT (nuclear protein in testis) carcinoma (NC) is an aggressive carcinoma characterized by rearrangements of the NUT gene on chromosome 15q14. Histologically, it is a poorly differentiated carcinoma composed of monotonous, medium-sized, round cells with scant amphophilic or eosinophilic cytoplasm. Foci of abrupt keratinization are often seen. In this report, we compare the morphology of 2 cases of NC. The first case shows characteristic features of uniform, round epithelioid cells admixed with foci of abrupt keratinization. The second case demonstrates nests of epithelioid-polygonal cells that appear to be loosely cribriform within a mucoid stroma. Although considered rare, the actual incidence of NC may be underestimated, as it is likely that many go undiagnosed because the morphology deviates from what is typical. Our report demonstrates that NC should always be considered in any case of an undifferentiated carcinoma and should not be excluded if typical histologic and immunohistochemical features of squamous differentiation are lacking.