ABSTRACT
Optimal therapy for the growing number of patients with lenalidomide (LEN)-refractory multiple myeloma (MM) in first relapse remains poorly defined. We therefore undertook a randomized phase II study evaluating the efficacy and safety of combining the oral proteasome inhibitor ixazomib (IXA) with pomalidomide (POM) and dexamethasone (DEX) for this patient population. The overall response rate (ORR) for POM-DEX was 43.6% and 63.2% for IXA-POM-DEX. Depth of response, as measured by attainment of a very good partial response or better favored the triplet over the doublet, 28.9% vs 5.1%, respectively (p = 0.0063). A pre-planned interim analysis after 75% of the progression events had occurred demonstrated a progression-free survival (PFS) advantage favoring IXA-POM-DEX that crossed the predefined boundary of superiority, leading to release of the study results. With additional follow-up, the median PFS for POM-DEX was 7.5 months (95% confidence interval [CI] 4.8 - 13.6 months) vs 20.3 months for IXA-POM-DEX (95% CI 7.7 - 26.0 months, hazard ratio 0.437 [upper 90% bound = 0.657]). ORR and median PFS for the 26 of 30 eligible patients who crossed over from the doublet to the triplet at progression was 23.1% and 5.6 months, respectively. Overall survival was similar between the two groups. More hematologic toxicities were seen with the triplet, but non-hematologic adverse events were similar between the two arms. Our data support further testing of this all-oral triplet vs current standard triplet therapy in the context of phase III studies for patients with LEN-refractory disease in first relapse. This trial is registered at www.clinicaltrials.gov as NCT02004275.
ABSTRACT
Preclinical studies have demonstrated activity of the oral proteasome inhibitor (PI) ixazomib (IXA) in bortezomib-resistant multiple myeloma (MM) and synergy with immunomodulatory drugs. We therefore conducted a phase I/II study to establish the safety and preliminary efficacy of IXA with pomalidomide (POM) and dexamethasone (DEX) in lenalidomide (LEN)/PI-refractory MM. Dose escalation established a 4 mg dose of POM and IXA and 20/40 mg dose of DEX as the maximum tolerated dose. The phase II portion of the trial was redesigned and started anew after six patients had been randomized to IXA-POM-DEX due to a rapidly changing treatment landscape. Among the 29 evaluable LEN/PI-refractory patients treated with IXA-POM-DEX in phase I/II, the overall response rate (partial response or better) was 51.7% with a median duration of response of 16.8 months (range 56 days to 4.1 years), median progression-free survival of 4.4 months (95% confidence interval [CI]: 3.0-18.4), and median overall survival of 34.3 months (95% CI: 19.2 to not reached). Hematologic, gastrointestinal, and constitutional adverse events were common and consistent with the side-effect profiles of the individual agents. Our results support further evaluation of this all-oral regimen in relapsed/refractory MM.