Soluble interleukin-6 receptor as a prognostic factor in multiple myeloma

Interleukin-6 (IL-6) is a major growth factor for the clonal malignant plasma cells in multiple myeloma (MM). The effect of IL-6 may be enhanced by soluble IL-6 receptor (sIL-6R). As there is a clinical need for improved stratification of MM patients at diagnosis, we have studied the role of sIL-6R as a prognostic marker in 207 newly diagnosed MM patients. Serum sIL-6R concentration was above the upper reference limit in 47% of the patients at diagnosis. The concentrations of sIL-6R and two other prognostic factors, IL-6 and β-2 microglobulin (β2M), were all significantly higher in the patients who died within 3 years compared with those who survived. However, serum sIL-6R did not show linear correlation with IL-6 or β2M levels. In univariate logistic regression analysis sIL-6R was a significant predictor of 3-year mortality. Kaplan-Meier analysis showed that raised levels of sIL-6R were associated with shorter survival. When the patients were stratified into four groups according to their serum IL-6 and sIL-6R levels, the patients with normal serum levels of both parameters had clear survival benefit. As β2M was the most powerful prognostic factor in the multivariate analysis, the patients were also stratified according to their serum β2M and sIL-6R levels. The patients with raised levels of both β2M and sIL-6R had shorter survival than the patients in the other three groups. Thus, measurement of these parameters at diagnosis would help to stratify MM patients.