Bortezomib after dose-reduced allogeneic stem cell transplantation for multiple myeloma to enhance or maintain remission status

Objective We investigated the effect of at least two cycles of bortezomib (1.3 mg/m2 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 μL to 438 μL (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.