Serum Free Light Chain and Serum Heavy / Light Chain Ratios Are Independently Prognostic in Multiple Myeloma Patients.

Abstract 4880

Serum free light chain ratios (FLCr) are important prognostic markers in B cell malignancies and their measurement has recently been included in multiple myeloma (MM) international guidelines. In contrast, serum IgG and IgA concentrations are not prognostic in MM. Novel immunoassays have been developed which target the specific conformational, junctional epitopes between the heavy and light chains of the immunoglobulin making it possible to measure Ig'kappa and Ig'lambda and produce an Ig'kappa /Ig'lambda ratio. Here we describe the use of FLCr and heavy/light chain ratios (HLCr) to predict survival in MM patients.

Archived sera from a historic MRC and a more recent Velcade, Adriamycin, dexamethazone (PAD) MM trail were utilised and the data combined using each study as a categorical variable. 85 MRC and 73 PAD samples were analysed retrospectively using serum free light chain and serum heavy / light chain nephelometric assays (The Binding Site Group). Kaplan Meier curves and Cox regression analysis were constructed comparing the upper quartile to the lower three quartiles for involved intact immunoglobulin, FLC, HLC and FLC + HLC. All analysis was completed using SPSS v14.0.

FLCr and HLCr values were not correlated (Pearson's = -0.037 p=0.66). There was no significant difference in survival when comparing the lower three quartiles and upper quartile of the involved intact immunoglobulin (Hazard Ratio [HR]=1.16: p=0.585). However, comparison of the upper quartile to the lower three quartiles did reveal significant differences in survival times for FLCr (HR=2.16: p=0.003), HLCr (HR=1.94: p=0.01) and FLCr+HLCr (HR=3.34: p=0.001).

Intact immunoglobulin concentration was not prognostic in this study in keeping with current international prognostic guidelines. As with previously published data, FLCr was a prognostic indicator in MM (van Rhee 2007, Kyrtsonis 2007). It is likely FLCr is more predictive of outcome than the concentration of tumour FLC production (data not shown) because it includes a measure of immunoparesis. HLCr was an independent prognostic indicator of survival in this study. HLCr measurement may be superior to intact immunoglobulin in predicting outcomes because: 1) Changes in haematocrit and plasma volume in MM can cause Ig to change by more than 50% regardless of tumour production. 2) Serum IgG is susceptible to variable clearance rates (related to saturation of the FcRn receptor for IgG). 3) Ig measurements using serum protein electrophoresis or nephelometry include all or some of the non-tumour Immunoglobulins and may be non-linear. The summated FLCr and HLCr is a stronger prognostic marker than either measurement independently. This maybe because, as shown by Ayliffe (2007) myeloma cells can produce intact immunoglobulin, FLC or both. Therefore, in patients with very low intact immunoglobulin production and high FLC production, FLCr is likely to be the most prognostic marker and visa versa for patients with low FLC production.