Stem-cell transplantation in non-Hodgkin's lymphoma: improving outcome.

High-dose therapy with stem-cell transplantation is a potentially curative therapy for younger patients with relapsed aggressive non-Hodgkin's lymphoma (NHL) and is also under investigation in relapsed indolent NHL. There are, however, risks associated with this treatment strategy. Autologous stem-cell transplantation (ASCT) continues to be associated with a high risk of relapse, while graft-versus-host disease is a major limiting factor with allogeneic stem-cell transplantation. The presence of minimal residual disease (MRD) in the harvested, re-infused stem cells, or remaining in the patient following chemotherapy, is associated with relapse after ASCT. As a result, monitoring and eradicating MRD has become a major focus of many studies in NHL. Rearrangement and overexpression of the bcl-1 and bcl-2 genes are the hallmarks of mantle-cell and follicular lymphoma, respectively, and evidence suggests that they are promising surrogate markers of MRD. Polymerase chain reaction analysis is a sensitive methodology used to monitor the status of occult lymphoma cells bearing these genetic aberrations, and results from trials of ASCT have shown that clearance of bcl-1/JH- and bcl-2/JH-positive cells following treatment is associated with a significant improvement in outcome. Rituximab, the anti-CD20 monoclonal antibody, is increasingly used for in vivo purging and can effectively eradicate bcl-1/JH- and bcl-2-positive cells. If the encouraging preliminary results with rituximab are maintained with a longer follow-up, this agent could play a pivotal role in improving outcome after stem-cell transplantation in NHL.