P63-Negative Pulmonary NUT Carcinoma Arising in the Elderly: A Case Report.

Abstract Background: We herein describe a rare case of primary pulmonary NUT carcinoma with unusual clinical and pathological presentations. NUT carcinoma of the lung occurs near the hilum in younger adults with severe symptoms and is positive for p63. This is the first case to show negativity for p63 and is the oldest among previously reported cases of pulmonary NUT carcinoma. Case presentation: An 82-year-old man was referred for an incidental finding of an abnormal shadow at the peripheral apex of the right lung on computed tomography for a regular follow-up examination of renal cancer. Microscopically, small cell carcinoma was initially suspected; however, immunohistochemistry was not typical. NUT carcinoma with BRD4-NUT fusion was ultimately diagnosed using a NUT monoclonal antibody, fluorescence in situ hybridization, and RNA-seq. p63 protein expression was not detected. Conclusions: NUT carcinoma is rare, but lethal, and, thus, must not be overlooked. The present case suggests the importance of NUT immunohistochemistry in cases of small round cell tumors without clear lineage-specific differentiation, regardless of age, clinical symptoms, the tumor location, or p63 expression.