GA In NEwly Diagnosed Diffuse Large B Cell Lymphoma (GAINED)

This study is designed to investigate the interest of a new monoclonal antibody (GA101) versus rituximab and the interest of PET to identify early responders. Patients will receive either rituximab (standard treatment), either GA101 (study treatment), according to the randomization arm. The monoclonal antibody will be associated to a chemotherapy: CHOP or ACVBP according to site's choice.A PET scan will be done before inclusion, after 2 chemotherapy cycles, and after 4 chemotherapy cycles, to identify early patients responders, for who consolidation with ASCT is not required.