A case of gastric plasmacytoma: genetic analysis and immunofixation electrophoresis.

: A case of early gastric plasmacytoma in a 66-yr-old woman is reported. The demonstration of monotypic IgM lambda immunoglobulin in plasma cells infiltrating the gastric antrum contributed the histological diagnosis. Genetic analysis of the tumor cells confirmed the presence of a monoclonal neoplastic population of plasma cells in the tumor. Monoclonal immunoglobulin (IgM lambda) was demonstrated in serum, not by conventional immunoelectrophoresis, but by a highly sensitive immunofixation electrophoresis technique. Serum monoclonal immunoglobulin disappeared after subtotal gastrectomy. The value of immunofixation electrophoresis of serum protein and DNA analysis of tumor cells was emphasized for the diagnosis of gastric plasmacytoma.