Diagnosis and monitoring for light chain only and oligosecretory myeloma using serum free light chain tests

This study aims to guide the integration of serum free light chain (sFLC) tests into clinical practice, including a new rapid test (Seralite^® ). Blood and urine analysis from 5573 newly diagnosed myeloma patients identified 576 light chain only (LCO) and 60 non-secretory (NS) cases. Serum was tested by Freelite^® and Seralite^® at diagnosis, maximum response and relapse. 20% of LCO patients had urine FLC levels below that recommended for measuring response but >97% of these had adequate sFLC levels (oligosecretory). The recommended Freelite^® sFLC ≥100 mg/l for measuring response was confirmed and the equivalent Seralite^® FLC difference (dFLC) >20 mg/l identified. By both methods, ≥38% of NS patients had measurable disease (oligosecretory). Higher sFLC levels were observed on Freelite^® at all time points. However, good clinical concordance was observed at diagnosis and in response to therapy. Achieving at least a very good partial response according to either sFLC method was associated with better patient survival. Relapse was identified using a Freelite^® sFLC increase >200 mg/l and found 100% concordance with a corresponding Seralite^® dFLC increase >30 mg/l. Both Freelite^® and Seralite^® sensitively diagnose and monitor LCO/oligosecretory myeloma. Rapid testing by Seralite^® could fast-track FLC screening and monitoring. Response by sFLC assessment was prognostic for survival and demonstrates the clinical value of routine sFLC testing.