Patients with a negative interim-PET scan (part A of the trial) will be randomized to receive either another four cycles of the (R-)CHOP regimen (arm A1) or four cycles of the (R-)CHOP regimen plus two additional doses of rituximab (arm A2). Randomisation in part A of the trial was stopped when the number of patients required was reached (128 patients in each treatment arm). Since then patients have been uniformly treated according to arm A2.