Gastric plasmacytoma: an early lesion diagnosed with the aid of immunoperoxidase and immunogold techniques.

A case of gastric plasmacytoma in a 34-yr-old woman has been presented. The demonstration of monotypic intracytoplasmic immunoglobulin of IgM-kappa type in biopsy specimens by immunoperoxidase technique contributed the confident histological diagnosis. In the resected stomach, IgM-kappa monoclonal proliferation of plasmacytic tumor cell was also demonstrated in the lamina propria and in the perivascular space of the submucosa, which was distinct from plasma cells of polyclonal nature diffusely infiltrating in the adjacent mucosa. The double immunogold staining confirmed the presence of immunoglobulin IgM-kappa type in the distended rough endoplasmic reticulum of the tumor cell.