Primary gastric low-grade fibromyxoid sarcoma with FUS-CREB3L1 fusion – A hitherto undescribed origin of Evans tumor

Low-grade fibromyxoid sarcoma (LGFMS) is a rare soft tissue neoplasm with a deceptively benign histological appearance. Only several LGFMS cases originating from the gastrointestinal tract have been reported, but all of them are from the small intestine or colon. Here, we describe a case of gastric LGFMS that was proven to have a characteristic FUS-CREB3L1 fusion gene. A 54-year-old Japanese female complained of epigastralgia. Abdominal computed tomography revealed a solid mass probably originating from the lessercurvature of the gastric body and protruding outside the gastric wall. Under the clinical diagnosis of suspicious gastrointestinal stromal tumor of the stomach, gastric wedge resection including the tumor was done. The macroscopic finding showed a mass approximately 8.0cm in maximal diameter with white-tan cut surface, arising from the gastric wall. Histological examination revealed a mesenchymal tumor consisting of blunt spindle cells with occasional collagen rosettes and inflammatory cells. Tumor was immunohistochemically positive for MUC4 and the molecular analysis using formalin-fixed paraffin embedded tissue detected FUS-CREB3L1 fusion which is a minor fusion gene type in LGFMS. Thus, the pathological diagnosis of gastric LGFMS was confirmed. To the best of our knowledge, the present case is the first one of LGFMS arising from the stomach in the English literature.