Refractory Transformed Follicular Lymphoma

The goal of this Phase 2, open-label, multicenter clinical trial is to assess the efficacy and safety of accelerated ramp-up and fixed-dose subcutaneous epcoritamab combined with lenalidomide in adults with relapsed or refractory (R/R) large B-cell lymphoma (LBCL) following progression after second-line CAR T-cell therapy. The main question it aims to answer is : \- What is the overall response rate (ORR) after Cycle 2, or at premature treatment discontinuation (PTD), according to the 2014 Lugano Response Criteria? Participants will: * Receive subcutaneous epcoritamab administered according to an accelerated ramp-up schedule followed by fixed dosing, in combination with lenalidomide. * Undergo clinical evaluations, laboratory assessments, and PET-CT imaging to determine disease status based on the 2014 Lugano Response Criteria. * Continue study therapy for up to 48 weeks. * Enter a follow-up period of at least 24 months after the last dose to monitor long-term outcomes and safety. Approximately 55 adults will be enrolled across multiple centers in France. Eligible individuals must have R/R LBCL, including diffuse large B-cell lymphoma and other eligible LBCL subtypes, with progressive metabolic disease documented by PET-CT at least 1 month after second-line CAR T-cell therapy. The overall study duration is expected to be approximately 5 years.