Serum Levels of Soluble FLT3 Ligand in Patients with Active Multiple Myeloma Constitute Marker of Bone Marrow Plasma Cell Proliferative Activity

: The FLT3-ligand is a molecule implicated in hematopoiesis. The aim of the present study was to detect any possible connections between serum levels of FLT3-L and multiple myeloma (MM) proliferation markers, such as serum levels of interleukin-6 (IL-6), B-cell activating factor (BAFF), beta-2 microglobulin (B2M), CRP and LDH, as well the percentage of bone marrow infiltration and the plasma cells' proliferation marker Ki-67 PI. We measured the above parameters in 58 patients with active MM. All circulating markers were significantly higher in MM patients compared to controls (p < 0.001 for all cases), and all values were increasing in parallel with disease stage (p < 0.001 for all cases). Positive correlations between FLT3-L were noted with serum levels of BAFF (p < 0.003), IL-6 (p < 0.002), CRP (p < 0.0001), LDH (p < 0.001), and BM Ki-67 PI (p = 0.012), whereas only trends of correlation were noted with the B2M value and the percentage of infiltration. It seems that the increased serum levels of circulating FLT3-L, in parallel with MM activity, reflect their increased presence in the bone marrow microenvironment, probably as an effect of increased angiogenesis and myelosuppression. Consequently, they are potential markers of disease activity.