Cytologic findings of NUT midline carcinoma in the hilum of the lung.

Nuclear protein in testis (NUT) midline carcinoma (NMC) is a clinically lethal malignancy affecting all age group often located in the midline structures such as mediastinum, larynx and nasopharynx. It is characterized by chromosomal translocation between chromosomes 15 and 19 with the formation of chimeric gene BRD-NUT. We present the cytologic findings of NMC including the immunohistochemical stains performed. The patient is a 34-year-old man who presented with 1 month history of dyspnea and interscapular pain followed by nonproductive cough a week before consultation. He was initially diagnosed with pneumonia. Due to progression of symptoms, a chest CT scan was performed revealing a large hilar mass and mediastinal adenopathy. A core biopsy with touch preparations of the hilar mass was performed which revealed cohesive malignant cells with ovoid to elongated nuclei, fine to coarse chromatin pattern, irregular nuclear contour, prominent nucleoli, and scant ill-defined cytoplasm arranged in sheets and focally pseudoglandular pattern. Although focal nuclear overlapping and crush artifact were identified, karyorrhectic debris and mitotic figures were rare. Squamous differentiation was absent. The core biopsy showed discohesive malignant cells with tumor necrosis. No nuclear molding, glandular or squamous differentiation was identified. The tumor was immunoreactive for p63 and NUT with high Ki-67 (>80%). The tumor was negative for keratin, lymphoid, myeloid, neuroendocrine markers and S-100. This case emphasizes that cytologic features of NMC can mimic poorly differentiated, undifferentiated and neuroendocrine carcinomas and the importance of immunohistochemical stains especially NUT monoclonal antibody in arriving at the diagnosis.