Monoclonal antibody SGN-30 and CHOP chemotherapy: Beginning 1 week after completion of monoclonal antibody SGN-30 monotherapy, patients receive monoclonal antibody SGN-30 IV over 2 hours on day 1 and CHOP chemotherapy comprising cyclophosphamide IV over 1 hour, doxorubicin hydrochloride IV over 15 minutes, and vincristine IV over 15 minutes on day 1 and oral prednisone once daily on days 1-5. Treatment repeats every 21 days for 6-8 courses in the absence of disease progression or unacceptable toxicity.