This clinical trial is focused on studying a type of cancer called Diffuse Large B-Cell Lymphoma (DLBCL), specifically in patients whose disease has worsened or not responded to previous treatments. The study is testing a combination of two treatments: tafasitamab and lenalidomide. Tafasitamab is given through an intravenous infusion, which means it is administered directly into the bloodstream, while lenalidomide is taken orally in the form of capsules.

The purpose of the study is to evaluate the safety and how the body processes these medications when used together. Participants will receive a modified dosing schedule of tafasitamab, either once every two weeks or once every four weeks, combined with lenalidomide. The study will monitor the participants over a period to observe any side effects and to determine the most suitable dose of tafasitamab when used with lenalidomide.

Throughout the study, participants will be closely observed to track the occurrence and severity of any treatment-related side effects. Additionally, the study will assess how well the combination of tafasitamab and lenalidomide works in controlling the disease. This includes measuring the response of the cancer to the treatment and how long any positive effects last. The study aims to provide valuable information that could help improve treatment options for patients with relapsed or refractory DLBCL.