NUT midline carcinoma of the mediastinum showing two types of poorly differentiated tumor cells: a case report and a literature review.

Nuclear protein in testis (NUT) midline carcinoma (NMC) is an extremely aggressive carcinoma that is genetically defined by rearrangement of the NUT gene. Herein, we describe a case of NMC in a young Japanese man, and review 31 cases of NMC in the literature. The present case was of a massive tumor of the anterior and middle mediastinum in a 26-year-old man. The tumor included 2 types of poorly differentiated tumor cells and was immunohistochemically positive for the NUT-specific antigen, epithelial membrane antigen (EMA), cluster of differentiation 99 (CD99) antigen, CD45RO antigen, keratins, p63, and p40. The patient died 2 months after the initial diagnosis. At least two-thirds of the 31 NMC cases in the literature were immunohistochemically positive for EMA, p63, and AE1/AE3. However, some exceptional NMC cases are keratins-negative/CD99-positive like Ewing sarcoma or CD45RO-positive like the present case.