Usefulness of Nuclear Protein in Testis (NUT) Immunohistochemistry in the Cytodiagnosis of NUT Midline Carcinoma: A Brief Case Report

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Nuclear protein in testis (NUT) midline carcinomas are uncommon , recently described, fatal neoplasm that are characterized by rearrangement of the NUT gene on 15q14. 1 Since the first case of NUT midline carcinoma was reported as an undif-ferentiated carcinoma with a t(15;19) translocation in 1991, 2 more than 50 cases have been reported. 3 Because of the unique chromosomal translocation and predilection for occurrence in midline structures, they have been termed NUT midline carci-nomas. However, tumors outside the midline have been reported , including the salivary gland, bladder, and other sites. We encountered a case of NUT midline carcinoma confirmed by NUT specific immunohistochemistry (IHC) using cytologic and histologic specimens. Herein, we present the first case report on immunocytologic features of NUT midline carcinoma arising in the parotid gland. A 12-year-old boy without a significant past medical history presented with a parotid mass. The neck magnetic resonance imaging (MRI) revealed a 2.4-cm-sized mass with irregular margins in the deep subcutaneous fat layer of the right cheek (Fig. 1). Several other masses with similar characteristic signal changes as the right cheek mass were identified in the deep fat layer in the right mandibular angle and submandibular area. A fine needle aspiration was performed on the right cheek mass. The aspirated smear had a necrotic background and showed both syncytial tissue fragments and scattered single cells (Fig. 2). The smear showed tiny necrotic foci. The tumor cells were relatively small (nucleus about 9 µm, cytoplasm about 20 µm in the longest diameter) and had pale cytoplasm and indistinct cell borders. The tumor nuclei were ovoid with small nu-cleoli and the chromatin was evenly dispersed and hyperchro-matic. The nuclear membranes had slight irregularity with occasional grooves. Most single cells had naked nuclei and occasional mitotic figures were identified. Squamous or glandular differentiation was not evident. A right total parotidectomy with neck dissection was performed for tumor removal and pathologic confirmation of the tumor subtype. Microscopically, it revealed numerous tumor islands forming sheets or nests within the desmoplastic stroma (Fig. 3). The tumor cells had similar cytologic characteristics to those of the aspirated smear (Fig. 3). Metastasis to the cervical lymph nodes as well as perineural …