A dose escalation feasibility study of lenalidomide for treatment of symptomatic, relapsed chronic lymphocytic leukemia

•We report a Phase I study of lenalidomide in two cohorts of patients – relapsed/refractory CLL and maintenance therapy in CLL.•Overall response rates on the maximum tolerated dose of lenalidomide at 5mg were not high, but several patients were able to continue treatment for many months with stable disease.•Tumor flare occurred in over 50% of the patients with relapsed/refractory CLL being treated with lenalidomide, despite the low doses being utilized.