Serum bone sialoprotein as a marker of tumour burden and neoplastic bone involvement and as a prognostic factor in multiple myeloma

To test the potential of immunoreactive BSP, a non-collagenous bone matrix component, as a clinical guide in patients with plasma cell dyscrasias, serum BSP concentrations were measured in 62 patients with newly diagnosed multiple myeloma (MM) followed over a period of 4 years, in 46 patients with monoclonal gammopathy of undetermined significance (MGUS), in 71 patients with untreated benign vertebral osteoporosis (OPO), and in 139 healthy adults. Results were compared with clinical and laboratory data, including serum osteocalcin (OC), and urinary pyridinoline (PYD) and deoxypyridinoline (DPD) as markers of bone turnover. In MM, serum BSP, and urinary PYD and DPD were higher than in healthy controls and in MGUS or OPO (P< 0.001). BSP levels correlated with the bone marrow plasma cell content (r = 0.40, P< 0.001), and serum beta2-microglobulin (r = 0.31, P < 0.01). The differentiation of MM from healthy controls and from MGUS or OPO was highest for BSP. After chemotherapy, BSP reflected the response to treatment and correlated with the change in monoclonal protein (r = 0.55, P< 0.001). MM patients with normal baseline BSP levels survived longer than patients with initially elevated BSP values (P< 0.001, log rank test). Only serum monoclonal protein and BSP were independent predictors of survival. We conclude that in MM, BSP levels are associated with skeletal involvement and tumour cell burden. The quantification of serum BSP may be a non-invasive method for the diagnosis and follow-up, and may improve the prognostic value of conventional staging in MM.