Gastric Epithelioid Mesenchymal Tumor with the EWSR1::CREM Fusion Gene: A Case Report

In recent years, new molecularly defined tumor groups have been reported among tumors previously considered unclassifiable. Among them, gene fusions involving the CREB family of transcription factors, including cAMP-responsive element modulator (CREM), with genes encoding FET family RNA-binding proteins, such as Ewing sarcoma breakpoint region 1 (EWSR1), have recently been shown to be implicated in driving the pathogenesis of various tumor types. Here, we report our experience with a gastric mesenchymal tumor with epithelioid histology and an EWSR1::CREM fusion, which is rare but requires caution.

A 58-year-old man with epigastric pain underwent esophagogastroduodenoscopy, which revealed a submucosal tumor, 40 × 30 mm in size, at the greater curvature of the upper gastric body. Surgical resection was scheduled because of easy bleeding from the tumor and because biopsy could not establish a diagnosis. The tumor was clinically considered benign because there was no significant accumulation on positron emission tomography scans. Therefore, we performed a local resection of the stomach. Histologically, the tumor consisted of a proliferation of keratin-positive, relatively uniform epithelioid cells arranged in sheets, with a scattering of lymphoid follicles in the surrounding area. Based on a pathology consultation, the tumor was diagnosed as a mesenchymal tumor with EWSR1::CREM fusion.

We experienced a gastric epithelioid mesenchymal tumor with EWSR1::CREM fusion genes. Since a malignant course has been reported in similar tumors in the stomach and abdominal cavity, such patients require careful follow-up.