Schematic overview of study design. Part 1, a dose-escalation phase, included 4 dose cohorts of daratumumab (2, 4, 8, and 16 mg/kg) in 28-day cycles in combination with lenalidomide 25 mg orally on days 1 through 21 and dexamethasone 40 mg once per week. Daratumumab was administered once per week during cycles 1 and 2, once every 2 weeks during cycles 3 through 6, and once every 4 weeks thereafter. In part 2, daratumumab 16 mg/kg was administered by using the same dosing schedule as in part 1 in combination with lenalidomide and dexamethasone. IV, intravenous; p.o., orally.