A phase 1/2 study of ixazomib in place of bortezomib or carfilzomib in a subsequent line of therapy for patients with multiple myeloma refractory to their last bortezomib or carfilzomib combination regimen.

Identifying effective combination regimens is a high priority in multiple myeloma (MM), as most patients eventually become refractory to their current treatments. In this study, we investigated whether the proteasome inhibitor (PI) ixazomib could delay disease progression among patients who failed regimens containing another PI, bortezomib or carfilzomib. This phase 1/2, multicenter, open-label, nonrandomized study enrolled patients who were refractory to a previous regimen containing bortezomib or carfilzomib. Patients continued the other anti-MM drugs in the regimen at the same doses and frequencies. Patients with combination regimens with unknown maximum tolerated dose (MTD) of ixazomib were enrolled in phase 1, with ixazomib starting at 3 mg and then dose escalated to 4 mg. Patients on regimens with a known ixazomib MTD were enrolled in phase 2. Primary endpoints were overall response rate (ORR), clinical benefit rate (CBR), adverse events (AEs), and determination of maximum tolerated dose (MTD). Of the 46 patients enrolled, 39 were evaluable for efficacy. ORR and CBR were 12.8% and 17.9%, respectively. Ixazomib appeared to be well tolerated as a replacement for carfilzomib and bortezomib, with 23.9% of patients experiencing at least one grade ≥3 serious adverse event (SAE) and 37.0% experiencing at least one grade ≥3 AE. The most common grade ≥3 AEs were hyponatremia (8.7%), anemia (8.7%), dyspnea (8.7%), thrombocytopenia (6.5%), dehydration (4.3%), and pneumonia (4.3%). The results indicate that ixazomib is not an effective replacement for bortezomib or carfilzomib for patients with MM who have previously relapsed on other bortezomib/carfilzomib-containing regimens.