IgM-producing gastric plasmacytoma.

A case of gastric plasmacytoma is reported in an 81-year-old woman. Immunofluorescent and immunoelectrophoretic studies showed that the tumor cells produced IgM-lambda molecules, whereas no monoclonal immunoglobulin could be detected both in the serum and in the urine. Of more than 60 reported cases of gastric plasmacytoma, only a few reports referred to the production of monoclonal immunoglobulin by the tumor cells. This case is the first one of IgM-producing gastric plasmacytoma. Moreover, the produced IgM was found to be 7S-IgM. It is extremely rare that 7S-IgM alone is detected in the absence of 19S-IgM.