Kaplan-Meier plots of the time to progression in the lenalidomide plus dexamethasone and dexamethasone alone groups for patients with or without prior thalidomide exposure. The estimate of time to progression for the intent-to-treat population of the lenalidomide plus dexamethasone and dexamethasone alone groups. Len/Dex indicates lenalidomide plus dexamethasone; Dex, dexamethasone; and thal, thalidomide.