Serum Free Light Chain (FLC) Analysis: A Guiding Light in Monoclonal Gammopathy Management

Background Monoclonal free light chains (FLCs) were first reported by Dr. Henry Bence Jones over 150 years ago in the urine of patients with multiple myeloma. Now established as important tumor markers, they aid not only in the diagnosis of monoclonal gammopathies but also in their clinical management by indicating the response to treatment and persistence of residual disease. Content A particular focus over the past 15 years has been on the replacement of urine with serum analysis for monoclonal FLC measurement. Because of the limited sensitivity and practical constraints of urine assessment, a combination of serum electrophoresis and serum FLC analysis has been adopted by many laboratories as a first-line screen for patients with a suspected monoclonal gammopathy. Early myeloma diagnosis may translate into improved clinical outcomes, and a new study, iStopMM, is underway to ascertain the benefit of population-wide screening protocols for early detection of the disease in its asymptomatic phase. Laboratory algorithms that include measurement of both monoclonal intact immunoglobulins and FLCs are important for assessing possible changes in myelomic clones in response to treatment, and recent data from Intergroupe Francophone du Myelome trials validate serum FLC as a clinically relevant disease biomarker. Whether sensitive serum techniques such as FLC analysis can be used to guide the use of more invasive procedures for detection of minimal residual disease is the subject of emerging studies. Summary Here we review the current and evolving utility of serum FLC measurements for the management of patients with monoclonal gammopathies.