[Role of novel proteasome inhibitors in the treatment of relapsed/refractory multiple myeloma].

Multiple myeloma (MM) is a mature plasma cell neoplasm characterized by the excessive production of monoclonal antibodies and various cytokines. Therefore, MM cells are highly dependent on the ubiquitin-proteasome pathway and the well-differentiated unfolded protein response in the endoplasmic reticulum. Bortezomib, the first approved proteasome inhibitor (PI) for the treatment of MM, is widely used as a therapeutic agent for patients with MM, including newly diagnosed and relapsed/refractory (RR) cases. However, severe peripheral neuropathy and gastrointestinal disorders often occur during bortezomib treatment, which leads to inadequate treatment of MM owing to the interruption or reduction in bortezomib administration. Novel PIs, carfilzomib and ixazomib, have been developed as less toxic and more effective PIs than bortezomib, and these novel PIs are expected to be potent options for the treatment of RR MM. The use of novel PIs, which is based on the characteristics of each agent and the condition of each patient, is considered an effective treatment, and it can improve the outcomes in patients with RR MM, particularly those who cannot tolerate bortezomib.