Gastric plasmacytoma coexistent with plasma cell granuloma in a patient with gastric cancer.

We report a rare case of multiple gastric plasmacytomatous lesions at an early stage found incidentally in a stomach resected because of gastric cancer. The three lesions had different macroscopic features, showing depressed, submucosal, and nodular tumor-forming types. The smallest, a depressed lesion, produced IgG of the lambda and kappa types, and had a plasma-cell granuloma-like appearence, whereas the largest, a submucosal tumor, was formed by the monoclonal proliferation of atypical plasma cells containing IgA-kappa type immunoglobulin, and the nodular lesion exhibited histological features intermediate between those of the other two lesions. From their microscopic features and the profile of immunoglobulin production, we believe that these lesions may represent different stages in the possible course of development of plasmacytoma from the early stage of plasma cell granuloma. All three lesions were located far from the gastric carcinoma and it was unclear whether they had any causal relationship with it.