The Role of Serum Free Light Chain and M-Protein Measurements in Determining Recurrent Disease in Multiple Myeloma After Stem Cell Transplantation

Abstract

The detection of reoccurrence of multiple myeloma (MM) after stem cell transplant (SCT) is usually carried out by the use of serum and urine protein electrophoresis and immunofixation. We retrospectively studied the utility of serum free light chain assay (sFLC) in a population of post-SCT MM patients and compared it to traditional methods with serum protein electrophroesis (SPEP). We compared the value of sFLC vs SPEP for predicting reoccurrence and for earlier detection. We analyzed consecutive 24MM patients diagnosed between 2004 and 2009, who underwent SCT with concomitant follow-up with sFLC and M-protein from 2004 to 2012. An elevated M-protein was indicated by a level ≥0.2g/dL. An abnormal sFLC was indicated by a κ:λ ratio >1.65 or <0.26 accompanied by an increase of >10mg/dL of sFLC from the baseline. Of the 24cases, 22 had intact immunoglobulin MM (16IgG, kappa; 2IgG lambda; 2IgA lambda; 2IgA kappa) and 2cases had light chain MM. All 24cases (100%) achieved a complete response or partial response to SCT as defined by the International Myeloma Working Group (IMWG). After SCT, 4(16.7%) MM patients remained in remission. 12(50.0%) patients had a recurrence of MM with measurable increases in both sFLC and M-spike, 5(20.8%) with increase in sFLC only and 3(12.5%) with increase in M-spike alone. Among the 20 patients with reoccurrence after SCT, 35% had earlier detection of sFLC than M-spike, 10% had M-spike detected before sFLC, 15% had concurrent elevated sFLC and M-spike, 25% had elevated sFLC only, and 15% had elevated M-spike alone. The medium time period for detecting the elevated sFLC or M-spike in patients undergoing reoccurrence after SCT was 3-6months vs. 6-9months (p-value: 0.0386; Mann-Whitney one-sided test). Our study concludes that sFLC should be used in conjunction with clinical and other traditional measures for the earliest detection of MM recurrence to ensure that the diagnosis is not missed by using SPEP assay alone.