Patients receive CHOP chemotherapy comprising cyclophosphamide IV over 15 minutes, doxorubicin IV, and vincristine IV on day 1 and oral prednisone on days 1-5. Patients with CD20-positive disease also receive rituximab IV on day 1 (or day 0 during course 1 only). Treatment repeats every 3 weeks for 5 courses in the absence of disease progression or unacceptable toxicity.