Several groups have reported a relatively high incidence of κ/λ sFLC ratio abnormalities ranging from 36 to 77% . Furtado et al.  characterised sFLCs in a cohort of 20 relapsed/refractory MCL patients enrolled into a clinical trial of single agent oral lenalidomide. At disease relapse, 8 of 20 (40%) MCL patients had elevated sFLCs concentrations (classed as monoclonal [7/20] or polyclonal [1/20]). Overall survival was significantly shorter in patients with abnormal sFLC ratios than in those with normal sFLC ratios (p=0.001, Figure 31.9). For patients with an elevated sFLC ratio at trial entry, a 35% rise in the sFLC ratio correlated with disease progression. Summated κ + λ sFLCs (ΣFLC) did not correlate with disease outcome.
Furtado et al.  also recorded serial sFLC measurements following lenalidomide treatment. In five patients with monoclonal FLCs at disease relapse, normalisation of the sFLC ratio correlated with clinical improvement (reduction in lymph node size and/or resolution of ‘B’ symptoms). Of the patients with normal sFLC ratios at disease relapse, four individuals subsequently developed a polyclonal elevation of κ or λ sFLCs . In such cases, the κ/λ sFLC ratio remained uninformative, but ΣFLC correlated with disease behaviour (Figure 31.10). Use of the κ/λ sFLC ratio for monitoring response to treatment has been reported in other patients .