Circulating monotypic B-cells in multiple myeloma: association with lambda paraproteins.

The peripheral blood and bone marrow mononuclear cell immunophenotype was investigated in series of 41 patients with plasma cell dyscrasias (29 with multiple myeloma and 12 with monoclonal gammopathy of undetermined significance (MGUS) or solitary plasmacytoma). A statistically significant relationship between the presence of monotypic B-cells (MBC) in the peripheral blood and the paraprotein light chain isotype was found in the myeloma patients (P = 0.0025). MBCs were documented in 71% of patients with lambda paraproteins, compared with only 13% of patients with kappa paraproteins. The difference in MBC was independent of disease stage as well as of individual prognosticators such as haemoglobin, renal function, paraprotein size and beta-2-microglobulin, although lambda producers had significantly higher calcium levels than patients with kappa paraproteins (P = 0.03). A similar trend was also noted for MBC to be found more commonly in patients with lambda producing MGUS and solitary plasmacytoma. This phenomenon may account for the worse prognosis in patients with lambda paraproteins. In our hands, immunophenotypic detection of peripheral blood involvement in plasma cell dyscrasias is more sensitive than investigation of karyotype or immunoglobulin gene rearrangements.