The short serum half-life of FLCs means that concentrations can fall rapidly if therapeutic treatment has been successful (Section 18.3.1). A number of studies have investigated the prognostic implications of an early sFLC response.
Hassoun et al.  monitored response in 42 MM patients and found that normalisation of the sFLC ratio after just one or two cycles of therapy was highly predictive for achieving CR or nCR (p=0.003). Dytfeld et al.  reported that a scoring system including ≥90% reduction in monoclonal immunoglobulin, ≥90% reduction in iFLC, or κ/λ sFLC ratio normalisation had >90% sensitivity and specificity for predicting patients going on to achieve a VGPR (n=40). Similarly, Hansen et al.  found an 80% reduction in iFLC at day 21 (after 1 cycle of treatment) gave a sensitivity of 87.5% and specificity of 100% for predicting VGPR (n=36) but noted that changes in the monoclonal immunoglobulin over the same period were not significantly different for those achieving VGPR or PR. Supportive data has also been published in various studies encompassing a number of different treatment modalities, with measurements taken during induction therapy , post ASCT  and in relapsed/refractory patients .
In contrast, Dispenzieri et al.  did not show any survival benefit of the sFLC response (defined as a 50% reduction in dFLC, iFLC or the κ/λ sFLC ratio), 2 months after initiation of therapy. However, it should be noted that the therapy used in this study did not include novel agents.