Mantle cell lymphoma (MCL) is a type of non-Hodgkin lymphoma (NHL) with aggressive disease characteristics resulting in multiple relapses after initial treatment. Lenalidomide is an immunomodulatory agent approved in the US for patients with relapsed/refractory MCL following bortezomib based on results from 3 multicenter phase II studies (2 including relapsed/refractory aggressive NHL and 1 focusing on MCL post-bortezomib). The purpose of this report is to provide longer follow-up on the MCL-001 study (follow-ups were 6.8 [NHL-002], 7.6 [NHL-003], and 52.2 [MCL-001] months). The 206 relapsed MCL patients treated with single-agent lenalidomide (25 mg/day PO, days 1 to 21 every 28-days) had a median age of 67 years (63% >= 65 years), 91% with stage III/IV disease, and 50% with >= 4 previous treatment regimens. With a median follow-up of X, the combined best overall response rate (ORR) was 33% (including 11% with complete remission [CR]/CR unconfirmed CRu). Lenalidomide produced rapid and durable responses with a median time to response of 2.2 months and median duration of response (DOR) of 16.6 months (95% CI: 11.1%-29.8%). The safety profile was consistent and manageable; myelosuppression was the most common adverse event (AE). Overall, single-agent lenalidomide showed consistent efficacy and safety in multiple phase II studies of heavily pretreated patients with relapsed/refractory MCL, including those previously treated with bortezomib.