NUTM1-rearranged sarcoma arising in the descending colon presenting as a submucosal mass: a case report

Abstract Purpose NUT midline carcinoma family number 1 ( NUTM1) -rearranged sarcoma is extremely rare and characterized by NUTM1 gene rearrangement with variable morphological features. The gastrointestinal tract is one of the most common sites. These sarcomas showing similar histopathological findings have yielded poor clinical outcomes. Case presentation A healthy 52-year-old Japanese man presented with a solitary, localized submucosal mass, 3 cm in size, in the descending colon. Microscopically, the sarcoma comprised sheet-like proliferation of plump epithelioid/rhabdoid cells, fibrosarcoma-like spindle cells showing an intersecting fascicular pattern, and neoplastic cell nests in hyalinized stroma. Immunohistochemistry (IHC) revealed that sarcoma cells were diffusely positive for NUT. Fluorescence in situ hybridization (FISH) confirmed NUTM1 gene rearrangement. Recurrences in the retroperitoneum at 9 and 21 months after initial surgery were surgically excised. The histopathological features and the results of IHC and FISH for the sarcoma coincided with those of previously reported NUTM1 -rearranged sarcoma occurring in the colon. The sarcoma recurred three times within a short time after the initial surgery. Therefore, the behavioral aggressiveness and site in which the sarcoma arose were also consistent with those of NUTM1 -rearranged sarcoma in the colon. Of note, these recurrent sarcomas comprised only a plump epithelioid/rhabdoid cell component. Conclusion We reported here an unusual sarcoma with unexpected poor outcomes. Our case may provide additional useful information regarding this extremely rare sarcoma of colonic submucosal origin.