Serum free light chains in myeloma patients with an intact M protein by immunofixation: potential roles for response assessment and prognosis during induction therapy with novel agents.

The ascertainment of serum free light chain (sFLC) levels has been shown to be valuable in screening for the presence of plasma cell dyscrasia as well as for baseline prognosis in newly diagnosed patients. For patients with amyloidosis and those with oligo-secretory or non-secretory multiple myeloma (MM), serial measurement of sFLC has also been shown to be valuable in monitoring disease status. However, in patients with a measureable, intact monoclonal protein by immunofixation (M protein), the serial measurement of sFLC remains undefined and is currently not recommended in professional guidelines. Herein, we provide data comparing sFLC with M protein as biomarkers of response in newly diagnosed patients with MM undergoing induction therapy with the novel agents thalidomide, lenalidomide and/or bortezomib. We show that although M protein appears to outperform sFLC comparatively over the course of induction therapy, the addition of FLC to M protein further informs the characterization of residual disease status post-induction. Moreover, sFLC at the time of stem cell mobilization appears to hold prognostic power for survival endpoints following high-dose chemotherapy/autologous stem cell transplant (HDC/SCT). These findings suggest potentially novel roles for sFLC in patients with MM with an intact M protein receiving novel agent-based induction strategies followed by HDC/SCT.