NUT carcinoma of the parotid gland: report of two cases, one with a rare ZNF532-NUTM1 fusion.

Nuclear protein in testis (NUT) carcinoma (NC) is a rare aggressive tumor with a typical NUTM1 gene rearrangement. Herein, we aimed to investigate the morphological and genetic features of head and neck NC. Immunohistochemistry staining for NUT (C52B1) was performed for 118 samples of head and neck poorly differentiated/undifferentiated carcinoma. Diffuse NUT staining was further confirmed via fluorescence in situ hybridization and next-generation sequencing. Two parotid gland NC cases, one in a 22-year-old man and one in a 52-year-old woman, were confirmed (2/118, 1.6%). Typical morphological features, including squamous cells and abrupt keratinization, were observed. Diffuse pankeratin, CK5/6, p63, and MYC expression were noted, while CD34, CD99, synaptophysin, chromogranin A, TTF1, S-100, and PD-L1 staining and EBER in situ hybridization (EBV-ISH) were negative. Both tumors harbored a NUTM1 rearrangement: a classic BRD4-NUTM1 fusion and a rare ZNF532-NUTM1 fusion. Furthermore, trisomy 8 and three copies of the MYC gene were detected in both cases. Next-generation sequencing revealed six additional somatic alterations, a low tumor mutation burden, and microsatellite stability. Patient 1 died from the disease after 15 months, and patient 2 was alive after 8 months. Parotid gland NC exhibits diverse morphological features and heterogeneous genotypes. To the best of our knowledge, this is the first report of parotid gland NC with a ZNF532-NUTM1 fusion.