Patients with biopsy-confirmed disease progression OR relapse after first-line treatment on this study or on protocols DAL-HD 90, GPOH-HD 95, GPOHHD 2002 Pilot, or similar treatment proceed to second-line therapy. Patients are stratified according to relapse/progression status (late relapse from first-line treatment group 1 [second-line treatment group 1] vs early relapse from first-line treatment groups 1, 2, or 3 or late relapse from first-line treatment groups 2 or 3 [second-line treatment group 2] vs disease progression [second-line treatment group 3]). Patients undergo a ^18FDG-PET scan prior to beginning second-line therapy.