This clinical trial is focused on studying a type of cancer called follicular lymphoma, which is a form of non-Hodgkin lymphoma. The study is investigating the effectiveness and safety of different treatment combinations for patients who have experienced a return or persistence of this cancer after receiving at least one previous treatment. The treatments being studied include a combination of Mosunetuzumab and Lenalidomide, and a combination of Rituximab and Lenalidomide. Mosunetuzumab is administered as a solution for infusion, which means it is given directly into the bloodstream through a vein, while Lenalidomide is taken orally in the form of capsules. Rituximab is also given as an infusion.

The purpose of the study is to compare how well these treatment combinations work in controlling the disease and to assess their safety. The study is divided into different parts, with some patients receiving Mosunetuzumab and Lenalidomide, and others receiving Rituximab and Lenalidomide. There is also a part of the study where all patients receive Mosunetuzumab and Lenalidomide without randomization. The study will monitor the patients over a period to see how the treatments affect the progression of the disease and to observe any side effects that may occur.

Throughout the study, patients will receive regular check-ups and assessments to track their response to the treatment. The study aims to provide valuable information on the best treatment options for managing follicular lymphoma, helping to improve outcomes for patients with this condition. The trial is expected to continue until 2029, allowing for comprehensive data collection and analysis.