The purpose of this study is to investigate and characterize the association of lenalidomide with tumor flare reaction and high tumor burden in participants with relapsed or refractory mantle cell lymphoma.

This is a European multinational, retrospective, non-interventional study of participants with relapsed or refractory mantle cell lymphoma (R/R MCL). Potential sites will be identified where R/R MCL participants have been treated with lenalidomide. Site inclusion will be limited to countries where lenalidomide is reimbursed for this indication.

Inclusion Criteria:

Received at least one dose of lenalidomide commencing after 08 July 2016 for the treatment of relapsed refractory mantle cell lymphoma.

Informed consent of the patient or an authorized third person or authority, if required by law, given prior to data collection.

Patient must be ≥18 years of age at the time of signing the informed consent form.

Exclusion Criteria:

1) Patients will be excluded if they were participating in an interventional clinical trial during the treatment period under observation in this Post Authorization Safety Study.

The study population will consist of a retrospective cohort of participants with refractory mantle cell lymphoma (R/R-MCL) who have commenced treatment with lenalidomide after 08 July 2016 (date marketing authorization was granted). Three datasets will be described for the study population and will form the basis of subsequent analyses: Population dataset, Treatment dataset, Outcomes dataset