Clinicopathological characteristics of primary lung nuclear protein in testis carcinoma: A single‐institute experience of 10 cases

BACKGROUND: Nuclear protein in testis (NUT) carcinoma is a rare tumor associated with NUT rearrangement that can present as poorly differentiated to undifferentiated carcinoma, with or without abrupt squamous differentiation. It is often misdiagnosed as poorly differentiated carcinoma or undifferentiated carcinoma if NUT is not suspected. In this study, we retrospectively analyzed pulmonary NUT carcinoma cases diagnosed with NUT immunohistochemical staining and discuss the differential diagnosis to provide information for this rare and aggressive entity. METHODS: Cases, diagnosed as “NUT carcinoma” in lung pleura and “metastatic NUT carcinoma from the lung” in lymph nodes were diagnosed between 2017 and 2019 at the Samsung Medical Center (SMC). Clinical features such as age, sex, treatment and follow‐up period, and pathological reports were obtained by reviewing patients’ electronic medical records. RESULTS: A total of 10 NUT carcinoma cases were found in the SMC pathology database. Seven patients were men and six were non‐smokers. Tumor cells showed various cellular features such as round, squamoid, and spindle. Some cases had initially been misdiagnosed as spindle cell neoplasm, round cell sarcoma, squamous cell carcinoma and small cell carcinoma. All cases showed diffuse strong nuclear expression of NUT immunohistochemical staining, and some were positive for p63 staining and negative for CD56 staining. CONCLUSIONS: NUT carcinoma is often misdiagnosed because of its various morphologies. It is important to consider NUT as one of the differential diagnoses when encountering lung biopsy with undifferentiated morphology. KEY POINTS: Due to various morphological features, NUT carcinoma can be misdiagnosed. It is important to consider NUT carcinoma when diagnosing a poorly differentiated or undifferentiated tumor.