NUT Carcinoma in the Pelvic Cavity With Unusual Pathologic Features.

NUT carcinoma is an aggressive epithelial malignancy defined by NUTM1 translocation, usually arising in the head/neck or thorax regions and showing squamous differentiation. Herein, we describe an extraordinary case of NUT carcinoma in the pelvic cavity. The patient was a 54-yr-old woman who was found to have a large pelvic mass with multiple metastases, suggestive of advanced ovarian cancer. Peritoneal seeding nodules were resected and subjected to pathologic examination. Upon microscopic investigation, infiltration of tumor cells showing monotonous-round morphology without squamous features was observed. Immunohistochemical analysis revealed faint/dot-like expression of cytokeratin, focal expression of vimentin, and diffuse expression of the estrogen receptor, but there was no detection of p40, p63, and Myc. NUT was diffusely and strongly expressed in nuclei, in which it exhibited a speckled pattern. Subsequent dual-color break-apart fluorescence in situ hybridization of NUTM1 confirmed a genetic translocation. Next, target-enriched next-generation sequencing covering ~200 major cancer-associated genes found no other significant alterations. After 2 cycles of chemotherapy, bilateral pleural effusion developed that were diagnosed as metastatic NUT carcinoma. The data suggest that NUT carcinoma should be enlisted in the differential diagnosis of poorly differentiated malignancies arising in the pelvic organs.