Diagnostic exercise: Submucosal gastric masses in a cat

A 14-year-old neutered male cat presenting with chronic vomiting had 2 masses within the submucosa of the stomach that were excised. They presented histologically as circumscribed, submucosal masses consisting of diffusely arranged medium-sized round cells with a moderate amount of cytoplasm and interspersed eosinophils, separated by trabecular fibroblastic stroma. The overlying mucosa was diffusely infiltrated by the same round cells, and marked epitheliotropism was present. Neoplastic cells labelled positive for CD3 and negative for CD79a and CD117. Giemsa staining and silver staining (SNOBA) were also negative. A T-cell lymphoma with reactive fibroplasia was diagnosed, and differential diagnoses including mast cell tumor and feline gastrointestinal eosinophilic sclerosing fibroplasia could be excluded.