 Patients receive prednisone orally PO twice daily BID on days 1-5; rituximab intravenously IV on day 1; etoposide, doxorubicin hydrochloride and vincristine sulfate IV over 96 hours on days 1-4; and cyclophosphamide IV over 30-60 minutes on day 5. Patients then receive filgrastim subcutaneously SC once daily QD beginning on day 6 and continuing until absolute neutrophil count recovers. Treatment repeats every 21 days for 6 courses in the absence of disease progression or unacceptable toxicity. 