A Case of Unclassifiable Spindle Tumor of the Duodenum

Abstract

The patient was a 45-year-old man. He presented with black stools, and an upper gastrointestinal endoscopy revealed a duodenal tumor. Although the biopsy results showed no translocation of the SYT gene, immunostaining and histology suspected duodenal synovial sarcoma. A subtotal stomach-preserving pancreaticoduodenectomy was performed. The postoperative resection specimens did not show any SYT gene translocation, and synovial sarcoma was ruled out. EWSR1 translocation was observed, however, the fusion gene could not be detected by RNA sequencing. The histological findings suggested that his disease might fit the concept of “round cell sarcoma with EWSR1-non-ETS fusions”, but the final diagnosis was unclassifiable spindle cell tumor. The disease concept of “round cell sarcoma with EWSR1-non-ETS fusions” is a new classification established in 2020, and there are no reports on this classification in Japan. We report our experience of a spindle cell tumor of the duodenum, which is a valuable pathological result.