Observational Study of Lenalidomide in Subjects With Mantle Cell Lymphoma Who Failed Ibrutinib Treatment

Inclusion Criteria: 1. Understand and voluntarily sign an informed consent document (ICD), if applicable, prior to any collection of study-related data. 2. Males or females ≥ 18 years of age at the time of signing the ICD (if informed consent is applicable) 3. Diagnosis of Mantle Cell Lymphoma (MCL) as assessed by the investigator. A copy of a pathology report establishing the diagnosis of MCL must be available 4. Must have received at least one dose of ibrutinib and must have met at least one of the following criteria: A. Relapse: Subjects with relapse following initial response of CR to ibrutinib (or an ibrutinib-containing regimen). Subjects may have discontinued or completed ibrutinib treatment at the time of relapse, and there is no upper limit on the time between the last dose of ibrutinib to time of relapse. B. Progressive disease (PD): Subjects with PD following initial response of PR to ibrutinib (or an ibrutinib-containing regimen). Subjects may have discontinued or completed ibrutinib at the time of progression, and there is no upper limit on the time between the last dose of ibrutinib to time of progression. C. Refractoriness: Subjects with i. Best response of stable disease (SD) during treatment with ibrutinib (or an ibrutinib-containing regimen), and then subsequently had PD, or ii. Best response of PD at anytime while on ibrutinib (or an ibrutinib-containing regimen) D. Intolerance: Subjects requiring premature discontinuation of ibrutinib for reasons other than PD prior to the planned end of treatment. Potential reasons for premature discontinuation may include Adverse Event (AE) attributed to ibrutinib or inability to continue ibrutinib for other reasons. Subjects responding to ibrutinib treatment must have documented PD/relapse following discontinuation of ibrutinib. The reason for the premature discontinuation of ibrutinib will be recorded. Exclusion Criteria: * no exclusion criteria.