Immunoglobulin Heavy/Light Chain Quantification ? Update on a New Biologic Marker in IgA Multiple Myeloma

In IgA multiple myeloma (MM), monoclonal (M)-spike quantification by serum electrophoresis (SEP) encounters some limitations. Heavy/light chain (HLC) assay is a novel quantitative immunoassay allowing the measurement of IgAk and IgAλ concentrations. The aim of this study was to assess the performances of HLC assay to monitor disease, to detect progression and relapse and to evaluate residual disease in comparison with traditional routine tests. We compared IgA HLC assay to SEP, immunofixation electrophoresis (IFE), total IgA concentration and bone marrow (BM) immunophenotyping in a routinely follow-up of 40 IgA MM patients (594 serums samples). HLC assay correlated well with both total IgA and M-spike (when quantifiable) during the follow-up. IgAk/IgAλ ratio monitored progression disease more accurately than SPE. HLC ratio was slightly less sensitive than IFE in the early prediction of relapse. At the stage of complete response (CR), HLC ratio was in perfect agreement with IFE and BM immunophenotyping. Nevertheless, at the stage of near complete response (nCR), IFE and BM immunophenotyping were more sensitive in the assessment of residual disease. In the current study, IgA HLC assay was found more performant than SPE in the monitoring of partial response and the disease progression but less sensitive than IFE to predict early relapse or to evaluate residual disease.