Background: Serum free light chain (FLC) measurement has become an important marker for the management of multiple myeloma (MM). However, several analytical challenges remain unresolved. We compared the clinical performances of the Sebia FLC assay in MM to the Freelite assay.
Patients and methods: A total of 177 patients from the IFM DFCI 2009 trial were enrolled onto this study, with a total of 368 samples analyzed. At baseline, concordance of the involved to noninvolved FLC ratio (iFLC/niFLC) was evaluated. During therapy, comparison of the disease response assessments according to International Myeloma Working Group criteria was performed.
Results: Compared to Freelite, the Sebia FLC assay demonstrated lower results, with a proportional bias with increased values. We demonstrated that the Sebia equivalent of the iFLC/niFLC ratio of 100 was 16. During follow-up, agreement in response assessment was moderate (for light chains MM) to good (for intact immunoglobulin MM). In the context of relapse, the concordance was moderate, but longitudinal follow-up showed a similar kinetics.
Conclusion: The Sebia FLC assay provides inequivalent absolute results from the Freelite assay. Despite lower absolute FLC values, the kinetics of response and relapse is exactly the same. As with other FLC assays available, follow-up of MM with the same method is advisable.
Keywords: IMWG; κ/λ ratio.
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