Phase Ib dose-escalation study (PX-171-006) of carfilzomib, lenalidomide, and low-dose dexamethasone in relapsed or progressive multiple myeloma

Purpose: Carfilzomib, a selective proteasome inhibitor, has shown safety and efficacy in relapsed and/or refractory multiple myeloma. This phase I study in patients with relapsed or progressive multiple myeloma assessed the safety and tolerability of escalating doses of carfilzomib in combination with lenalidomide and low-dose dexamethasone (CRd) to identify the dose for a phase II expansion study. Experimental Design: Patients with multiple myeloma who relapsed after 1 to 3 prior regimens enrolled into dose-escalation cohorts. CRd was administered on 28-day dosing cycles: carfilzomib 15 to 27mg/m² on days 1, 2, 8, 9, 15, and 16; lenalidomide 10 to 25 mg on days 1 to 21; and dexamethasone 40 mg weekly. Results: Forty patients enrolled in six cohorts. Prior treatment included bortezomib (75%) and lenalidomide (70%);20%and36%were refractory overall. The maximum tolerated dose was not identified, and the highest dose combination tested was recommended for the phase II study. The most common toxicities of any grade were fatigue (62.5%), neutropenia (55.5%), and diarrhea (52.5%). Grade 3/4 toxicities included neutropenia (42.5%), thrombocytopenia (32.5%), and lymphopenia (27.5%), with no grade 3/4 neuropathy reported. Proteasome inhibition 1-hour after dose was more than 80% in cycles 1 and 2. Among all patients, the overall response rate was 62.5%, the clinical benefit response rate was 75.0%, and the median duration of response and progression-free survival were 11.8 and 10.2 months, respectively. Conclusion: The maximum planned CRd dose, carfilzomib 27 mg/m², lenalidomide 25 mg, and dexamethasone 40 mg, was recommended for further study, with promising safety and efficacy.