Serum bone gla-protein in multiple myeloma.

Serum bone gla-protein (SBGP), a marker of bone formation, was measured by radioimmunoassay in 57 patients with multiple myeloma (MM) and correlated with presenting features and disease activity. As a whole, patients with MM did not differ from normal controls or from patients with a monoclonal gammopathy of undetermined significance, but a significant percentage of abnormal values of SBGP was found in this MM population (18% of cases, P less than 0.005). At the time of diagnosis, SBGP was significantly lower in advanced disease (Stage III) than in less active disease (Stage I and II) with mean values of 4.4 +/- 2.7 ng/ml and 7.1 +/- 1.9 ng/ml, respectively (P less than 0.02). SBGP levels inversely correlated with the severity of the disease, the lowest values being observed in patients with extensive lytic bone lesions frequently associated with hypercalcemia (2.9 +/- 1.7 ng/ml). These data suggest the presence of a strong osteoblastic inhibition, at the body level, in the majority of patients (80%) with active osteoclastic MM (uncoupled process). However, a small subset of myeloma patients (20%) presented coupled MM, as defined by increased bone resorption (i.e., lytic bone lesions +/- hypercalcemia) and increased bone formation (i.e., increased SBGP values). Similar features of coupling-uncoupling were observed during disease progression. Finally, serial studies performed in 15 patients confirm these findings and the relation of SBGP levels to disease activity. Of major interest was the observation of a return of SBGP levels from low to normal values during remission induction, after successful completion of a plateau phase. According to these data, SBGP appears to be a new and promising marker for the clinical evaluation of MM.