COURSE B (COURSES 2, 4, AND 6): Patients receive brentuximab vedotin, dexamethasone, and methotrexate as in Arm BV, Course A. Patients also receive cyclophosphamide IV over 15-30 minutes on days 1-5 and doxorubicin hydrochloride IV over 1-15 minutes on days 4 and 5.