Immunoglobulin gene rearrangement in multiple myeloma: limitations of Southern blot analysis

Thirty-six patients with early and advanced multiple myeloma were investigated with Southern blot analysis to determine the presence of immunoglobulin gene rearrangement as evidence of clonality. Rearrangements were not uniformly found, being detected in only 14 of 19 patients with newly diagnosed myeloma and in 15 of 17 cases of clinically advanced myeloma. A correlation between percentage of bone marrow plasma cells and detection of immunoglobulin gene rearrangement was noted; however, in four cases of early myeloma with > 10% marrow plasma cells, no rearrangement was found. These results suggest that Southern blot analysis may not be an optimal method for the determination of clonality in plasma cell dyscrasias or, alternatively, that a proportion of the plasma cells found on bone marrow examination in some patients with early myeloma may not be monoclonal.