IgA-lambda/IgG-kappa biclonal myeloma in which two clones proliferated in individual sites

A 72-year-old man was admitted to our hospital because of lumbago and numbn ess of legs. Tumor invasion at the fourth lumbar vertebra was revealed. Imm unohistochemistry using specific antibodies against each heavy and light ch ain of immunoglobulin revealed that the myeloma cells in bone marrow were a ll IgA-lambda type whereas they were all positive for IgG-kappa type in a t umor of the fourth lumbar vertebra. These data indicate that the patient ha d IgG-kappa/IgA-lambda biclonal myeloma. Different phenotypes of M-proteins and distinct proliferating sites for two clones suggest that they may have resulted from two independent transforming events.