Multiple myeloma (MM) remains incurable and specially of poor prognosis in case of refractory or relapsed disease. However, recent therapeutic advances including the use of new drugs are promising. Although, Bortezomib, new proteasome inhibitor, has proven its efficacy in patients with refractory or relapsed MM, it has not been sufficiently evaluated in the setting of allogeneic hematopoietic stem cell transplantation. Here, we report four cases of MM patients, very heavily pre-treated and all previously transplanted, who received bortezomib associated to dexamethasone for relapse after allogeneic RICT (median time from diagnosis: 68 months, median time from RICT: 41 months). We studied the feasibility, efficacy and safety of bortezomib: two patients achieved a complete remission, one patient a very good partial response, and one had no response. The tolerance was excellent with only one patient who developed a reversible grade 3 hematological toxicity. No GVHD recrudescence was observed. All patients relapsed after completion of bortezomib treatment. This questions about the potential benefit of maintenance therapy with bortezomib. Given the feasibility and the high efficacy of bortezomib combined with dexamethasone in relapsed MM after RICT, our results argue in favour of an immune-modulatory activity of bortezomib. New strategies combining RICT and bortezomib are warranted to increase and maintain an adequate response. Combination RICT and bortezomib regimen are anticipated to further extend survival in relapsed MM.

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