Bortezomib is a novel
proteasome inhibitor that has shown marked antitumor effects in patients with
multiple myeloma (MM). We evaluated the feasibility and efficacy of
bortezomib plus
dexamethasone (BD)
therapy and assessed bone metabolism in relapsed or refractory MM. Fourteen patients received 1.3 mg/m2
bortezomib on days 1, 4, 8, and 11 along with 20 mg/dose of
dexamethasone on days 1, 2, 4, 5, 8, 9, 11, and 12 in a 21-day cycle. After 1 to 3 cycles of BD
therapy, 9 patients (64%) achieved an objective response (5 very good partial responses and 4 partial responses). Notably, a rapid increase in the serum concentration of
alkaline phosphatase (ALP) was observed in 6 of the treatment-responsive patients. Moreover, serum levels of bone-formation markers (bone-specific ALP and
osteocalcin) significantly increased in 5 and 2 responsive patients, respectively. Radiographic examination showed improvement in bone lesions, suggesting that BD
therapy induces osteoblast activation in responders. Adverse events included
thrombocytopenia of grades 1 to 3,
peripheral neuropathy of grades 1 to 2, and grade 3
ileus and were transient and manageable. Although severe
lung injury has been reported among Japanese patients treated with
bortezomib, no pulmonary complications were observed during BD
therapy. Our results suggest that BD
therapy is a safe and promising therapeutic approach for Japanese patients with MM.