Evaluation of Treatment by Glofitamab in Combination With Rituximab or Obinutuzumab Plus CHOP in Patients With RIchter Syndrome

This is a national clinical trial, multicentric (28 centers), non-randomized phase 2 study. Population: Patients with previously untreated Richter's syndrome (RS), defined as the occurrence of an aggressive lymphoma (of diffuse large B-cell lymphoma histology) in a patient with chronic lymphocytic leukemia (CLL). Study treatment: The duration of each cycle is 21 days. Cycle 1: Participants will receive standard of care doses of R-CHOP in cycle 1 as follows: * Rituximab 375 mg/m² IV Day 1 * Cyclophosphamide 750 mg/m² IV Day 1 * Doxorubicin 50 mg/m² IV Day 1 * Vincristine 1.4 mg/m² \[capped at 2.0 mg\] IV Day 1 * Prednisone 60 mg/m2 per day PO Day 1-5 Cycle 2: In order to minimize cytokine release syndrome (CRS), participants will then receive G-CHOP as cycle 2 (with obinutuzumab) and glofitamab: * Obinutuzumab 1000 mg single dose IV Day 1 * Cyclophosphamide 750 mg/m² IV Day 1 * Doxorubicin 50 mg/m² IV Day 1 * Vincristine 1.4 mg/m² \[capped at 2.0 mg\] IV Day 1 * Prednisone 60 mg/m2 per day PO Day 1-5 * Glofitamab : administered intravenously (IV) as a step-up dose on Days 8 (2.5 mg) and 15 (10 mg) Cycle 3-6: Participants will receive standard of care doses of R-CHOP and Glofitamab as follows: * Rituximab 375 mg/m² IV Day 1 * Cyclophosphamide 750 mg/m² IV Day 1 * Doxorubicin 50 mg/m² IV Day 1 * Vincristine 1.4 mg/m² \[capped at 2.0 mg\] IV Day 1 * Prednisone 60 mg/m2 per day PO Day 1-5 * Glofitamab : 30 mg IV Day 8 Cycle 7 and 8 (only for patient in Complete Response or Partial response after Cycle 6): Cycle 7 and 8 consist of 2 infusions of glofitamab only at D8C7 and D8C8: ● Glofitamab : 30 mg IV Day 8 Primary endpoint Percentage of participants with a complete response as assessed by the investigator using the Cheson IWG 2014 Lugano Classification (i.e. Deauville scale 1-3) after 6 cycles of R/G-CHOP + glofitamab or at permanent treatment discontinuation. End of treatment is defined as after 6 cycles of R/G-CHOP + glofitamab. Permanent treatment discontinuation is defined as the discontinuation of all treatments (R/G-CHOP, glofitamab).