[Primary pulmonary NUT carcinoma: a clinicopathological analysis of seven cases].

Objective: To investigate the clinicopathological characteristics of primary pulmonary NUT carcinoma. Methods: A total of 7 cases of primary pulmonary NUT carcinoma were collected from Fujian Provincial Hospital (n=5), Fuzhou Taijiang Hospital (n=1) and Binzhou City People's Hospital of Shandong Province (n=1) from January 2021 to April 2023. The clinical, histopathological, and immunohistochemical features were analyzed, and NUT rearrangement were detected by fluorescence in situ hybridization (FISH) with break-apart probes. Results: Seven cases were all male with age ranging from 32 to 73 years. The main clinical manifestations were cough, expectoration and chest tightness. Microscopically, NUT carcinoma was composed of monotonous proliferation of primitive-appearing small-to-medium round cells, with few eosinophilic cytoplasm, arranged in solid sheets, nests or clusters. Abrupt keratinization was typically observed in 4 cases (4/7), with high mitotic activities and necrosis. Immunohistochemistry (IHC) showed that the tumors were positive for NUT (7/7), CK7 (4/4), CK5/6 (5/6), p40 (6/7). Ki-67 index were 30%-80%. NUT gene segregation (7/7) was detected by FISH break probes. Conclusions: Primary pulmonary NUT carcinoma is rare and highly malignant. Diagnosis depends on histopathology and IHC, with molecular detection as an adjunct for diagnosis. Pathologists should be aware of the clinicopathological characteristics to avoid misdiagnosis.