Bortezomib increases osteoblast activity in myeloma patients irrespective of response to treatment

: Objectives: Myeloma bone disease is a result of excessive osteoclast activation and impaired osteoblast function. Recent in vitro studies suggested that proteasome inhibitors might increase osteoblast function. Methods: We analyzed serum markers of osteoblast activity in 25 patients with multiple myeloma receiving bortezomib alone or in combination with dexamethasone. As control, serum samples from 58 consecutive myeloma patients receiving a therapy different than bortezomib (i.e. adriamycin/dexamethasone, melphalan/prednisone or thalidomide) were evaluated. The serum concentrations of bone‐specific alkaline phosphatase (BAP) and osteocalcin were quantified before initiation of treatment and after 3 months. Results: In patients treated with bortezomib, mean serum levels of osteocalcin significantly increased from 6.3 to 10.8 μg/L (P = 0.024), while mean BAP levels increased from 19.7 to 30.2 U/L (P