- Rituximab and Combination Chemotherapy (R-CHOP: R= Rituximab, C= Cyclophosphamide, H= Doxorubicin Hydrochloride (Hydroxydaunomycin), O= Vincristine Sulfate (Oncovin), P= Prednisone): Patients receive rituximab IV, cyclophosphamide IV, doxorubicin hydrochloride IV, and vincristine IV on day 1, and oral prednisone once daily on days 1-5. Treatment repeats every 21 days for 4 courses in the absence of disease progression or unacceptable toxicity. Patients undergo fludeoxyglucose F18 positron emission tomography (PET) scanning and conventional restaging during course 3. Based on the PET results, patients are assigned to 1 of 2 treatment groups.