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.
Moritz et al.  assessed the prognostic value of changes in serum M-protein and sFLC measurements in 358 MM patients (n=85 newly diagnosed and 273 relapsed/refractory) with measurable disease (Section 25.3.5). Values were compared before and after the first treatment cycle, and categorised according to the degree of M-protein/sFLC reduction. Patients who had no response in either marker (M-protein: 87/358; dFLC: 117/358) were less likely to respond to treatment later on (both p<0.001) and had a shorter median survival (M-protein: 2.9 vs. 4.7 years, p<0.005; dFLC: 1.8 vs. 5.2 years, p<0.001) compared to patients with some degree of response. Importantly, greater decreases in M-protein and dFLC were associated with increased odds of better responses during the same treatment course and better overall survival. These findings are in contrast to an early study by the same group , which did not show any survival benefit of the sFLC response. However, it should be noted that the therapy used in the earlier study did not include novel agents.
There is now overwhelming evidence that confirms the prognostic value of reductions in sFLCs following therapy. Such evidence has been published in various studies encompassing a number of different treatment modalities, including non-transplant patients  and transplant patients with measurements taken during/post induction therapy  and post ASCT , and also in relapsed/refractory patients .