Triclonal gammopathy (IgA kappa, IgG kappa, and IgM kappa) in a patient with plasmacytoid lymphoma derived from a monoclonal origin.

We report the case of a 64-year-old woman with plasma cytoid lymphoma of the ileum and gastric wall. Serum protein electrophoresis and immunoelectrophoresis showed a triclonal IgG kappa, IgA kappa, and IgM kappa gammopathy. Biopsy of the tumor revealed three different cell types, which were stained with antibodies specific for IgG, IgA, and IgM. However, DNA analysis of immunoglobulin gene rearrangements using JH, C mu, and C kappa gene probes showed a monoclonal pattern. These results suggest that the three types of malignant cells producing different classes of immunoglobulins were derived from a single clone of B-cells that had undergone a "class switch".