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.