Interleukin-6 in multiple myeloma: correlation with disease activity and Ki-67 proliferation index

Interleukin-6 (IL-6) is supposed to be a growth factor in multiple myeloma (MM). Applying a bioassay and a modified ELISA, we measured serum IL-6 values in 64 patients with overt MM, seven patients with smouldering myeloma (SMM), 57 patients with monoclonal gammopathy of undetermined significance (MGUS) and 40 healthy volunteers as controls. IL-6 failed to discriminate between MGUS and MM, stage I, whereas comparison of MM, stage I and stage II/III (p = 0.0143), or comparison of stable disease/remission and progressive disease (p < 0.0001) revealed significant differences. Furthermore, we found significantly higher IL-6 values in overt MM compared to SMM (p = 0.0018). Using a Ki67/CD38 immunohistological double staining method we found a significant correlation between proliferation of bone marrow myeloma cells and serum IL-6 values in 15 patients (p = 0.005). These data demonstrate that IL-6 is a parameter of disease activity in MM and, beside its role in tumor biology, may become a valuable supplement to the established risk factors when selecting patients with unfavourable clinical course for more aggressive treatment modalities.