OBJECTIVE: We investigated the effect of at least two cycles of bortezomib (1.3 mg/m(2) intravenously, days 1, 4, 8, and 11) after dose-reduced allogeneic stem cell transplantation (SCT) on toxicity, CD3(+) cells, graft-versus-host disease (GvHD), and response in patients with multiple myeloma. METHODS: Eighteen patients with multiple myeloma without progressive disease were included. The proteasome inhibitor was given at median of 8 months after allografting to enhance or maintain remission status. RESULTS: Fourteen patients (78%) completed the proposed two cycles. Four patients had to discontinue therapy due to neurotoxicity (n = 3) or gastrointestinal toxicity (n = 1). Severe grade III/IV toxicity was seen for thrombocytopenia (50%), leukopenia (17%), or neuropathy (17%), which was more often seen in patients treated concomitantly with cyclosporine (p = 0.06). The median circulating CD3(+) cells decreased during treatment from 550 muL to 438 muL (p = 0.03), resulting in herpes zoster infection in three patients (17%). In three patients, a mild aggravation of existing acute or chronic GvHD of the skin, and in one patient de novo skin grade I acute GvHD was noted. In patients with measurable disease, complete remission, partial remission, and minor response was seen in 3 (30%), 5 (50%), and 2 (20%) patients, respective. CONCLUSION: Bortezomib after allogeneic SCT is effective but further studies are needed to balance the efficacy with potential hazards such as infectious complications, aggravation of GvHD, and neurotoxicity.
