4. Must be refractory to lenalidomide, defined as having received at least 2 consecutive cycles of lenalidomide as a single agent or within a lenalidomide-containing regimen and having had PD during treatment with or within 60 days after the last dose of lenalidomide. The starting dose of lenalidomide should have been 25 mg (or as low as 10 mg in the case of renal function impairment or other safety concern), and the final dose should have been a minimum of 10 mg.