Serial serum free light chain measurements do not detect changes in disease status earlier than electrophoretic M-spike measurements in patients with intact immunoglobulin myeloma

BackgroundSerum free light chains (SFLC) are used to manage patients with light chain or hyposecretory myeloma, and may also be useful in patients with intact immunoglobulin myeloma (IIMM), because their shorter half-life may enable earlier indication of relapse/response than electrophoretic M-spikes or heavy chain (IgGA) immunonephelometry.MethodsOne thousand five SFLC, M-spike, and IgGA concentrations were compared at multiple time points during the treatment of 17 myeloma patients, followed over 7.7–63.4 months. Changes in these analytes were evaluated in context with changes in disease status and treatment.Results14/17 (82%) patients showed synchrony between M-spike, IgGA, and SFLC measurements. SFLC changes preceded M-spike/IgGA in 1 patient, and lagged behind M-spike/IgGA in 2 patients. In eight patients, SFLC showed short-term fluctuations unaccompanied by changes in M-spike, IgGA, or clinical treatment.ConclusionsIn 16/17 intact immunoglobulin myeloma patients tested frequently over ~ 3 years, SFLC performed no better than M-spike and did not add value to conventional serum electrophoresis.