Garcia de Veas Silva et al. [882] studied the prognostic value of sFLCs in 43 patients with LCMM. At diagnosis, patients with an involved sFLC concentration above the median value (κ LCMM: 413mg/L; λ LCMM: 985 mg/L) had a worse prognosis. The median overall survival was 45 months for patients with iFLC concentrations above the median value, and was not reached in those with levels below this value. A highly abnormal sFLC ratio at diagnosis (defined as >43 or <0.01 based on the median values for κ and λ patients, respectively) was also associated with a similar adverse outcome.

Reid et al. [331][332] determined the prognostic impact of abnormal sFLC ratios in LCMM patients who had become IFE-negative. In a preliminary analysis including 35 LCMM patients, they showed that an abnormal κ/λ sFLC ratio in IFE-negative patients had a negative impact on overall survival. In a separate study, Boyle et al. [336] assessed the prognostic significance of the sFLC response in 122 LCMM patients. Following treatment, patients who achieved both a normal κ/λ sFLC ratio and a normal involved FLC concentration (32/122; 26%) had a significantly longer progression free survival and overall survival compared to those with a normalisation of their ratio only (50/122; 41%) (p<0.001 and p=0.012, respectively). Both these groups had a better survival than the remaining 40 patients judged to have had a suboptimal response (p=0.012). These studies highlight the prognostic relevance of sFLC measurements in LCMM; sFLC responses are similarly prognostic in patients with intact immunoglobulin MM and this is discussed in more detail in Chapter 20.