About 60% of patients with DLBCL can be cured with a chemotherapy program. It is called RCHOP-21 (Rituximab, Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone). It is given once every 3 weeks, for 18 weeks. Each three weeks is a cycle. Some factors predict that you may not be cured with R-CHOP-21. The most common ones are: * Stage - how much DLBCL, PMBL, or FL3B you have * LDH - a blood chemistry marker; and * Whether you can do your normal daily activities. (performance status) We think that the best way to cure more patients with poor risk factors is to add new treatment to R-CHOP. You will get different chemotherapy after 4 cycles. This type of treatment is called risk-adapted therapy.