OUTLINE: This is a randomized, multicenter study. Patients are stratified according to response to pre-salvage chemotherapy (primary refractory disease vs relapse), response to post-salvage chemotherapy (complete/unconfirmed complete vs partial), and participating center. Within 6-8 weeks after completion of autologous hematopoietic stem cell transplantation, patients are randomized to 1 of 2 treatment arms.