Gastric Plasmacytoma with Immunoglobulin Lambda Light Chain Deposition in a Dog

A 12-year-old castrated male Jack Russell Terrier presented with intermittent vomiting. Abdominal ultrasonographic examination detected a thickened stomach wall with a mass measuring approximately 1.5 cm in diameter. Computed tomography revealed a solitary mass measuring approximately 2.1 cm in diameter between the submucosa and muscle layers in the greater curvature the pyloric region of the stomach, and a swelling in the hepatic lymph node. The gastric mass was composed of round neoplastic cells arranged in a diffuse pattern. The neoplastic cells had a round nucleus and a pale abundant cytoplasm. Multinucleated giant cells were often found. Hyalinized eosinophilic material, which did not stain with Congo red and had no affinity for thioflavin T, was also observed. Neoplastic cells were immunopositive for MUM1, CD79a and Ig lambda light chain but negative for CD3, CD20, BLA36, IgG and Ig kappa light chain. Stromal eosinophilic material was positive for Ig lambda light chain. The neoplasm was therefore diagnosed as a gastric plasmacytoma with non-amyloid Ig lambda light chain deposition.