A EWSR1-CREM-rearranged gastric mesenchymal tumor accompanied by gastritis cystica profunda and with probable benign behavior: a case report

Genomic rearrangements involving EWSR1 and the CREB family of transcription factors are increasingly detected in an array of mesenchymal neoplasms, most of which are malignant. Gastritis cystica profunda (GCP) is a rare disease characterized by cystic dilatation of gastric glands into the submucosa and generally regarded as a precursor to tumor. Herein, we report a peculiar case in which an EWSR1-CREM- rearranged gastric mesenchymal tumor was admixed with GCP in a 64-year-old woman. All layers of the gastric wall were invaded, although no lymph node or neural invasion, or tumoral vascular emboli was noted. The mass showed readily distinguishable epithelial and mesenchymal components. The epithelial component consisted mainly of glandular structures with some showing metaplastic growth. The epithelial cells showed focally atypical hyperchromatic nuclei, slightly eosinophilic cytoplasm, and infrequent mitosis. The mesenchymal component consisted of monomorphic, ovoid-shaped cells with scanty cytoplasm, regular nuclei, and rare mitotic figures. Immunohistochemically, the epithelial cells were uniformly positive for cytokeratins, and the mesenchymal neoplasm showed focal positivity for CD10, CD117 and CD56. An EWSR1-CREM fusion was identified with genomic profiling and confirmed with fluorescence in situ hybridization (FISH) in the tumor. Given the low mitotic activity, absence of nodal or distant spread and vascular or neural invasion, and disease-free status at 28-month follow-up, both lesions were likely benign. To our knowledge, this is the first to report an EWSR1-CREM fusion in a gastric mesenchymal tumor with accompanying GCP.