Controversies in autologous and allogeneic hematopoietic cell transplantation in peripheral T/NK-cell lymphomas.

Peripheral T-cell and NK-cell lymphomas (PT/NKCL) are a heterogeneous group of lymphoid neoplasms with poor outcomes. There is no consensus on the best front line therapy or management of relapsed/refractory disease. The use of autologous and allogeneic hematopoietic cell transplantation (HCT) has been studied in both settings to improve outcomes. Multiple retrospective and several prospective trials were reported. While at first sight the outcomes in the relapsed/refractory setting appear similar in B-cell and T-cell lymphomas when treated with high dose therapy (HDT) and autologous HCT, it is becoming obvious that only specific subtypes of PTCL benefit from this approach (i.e. anaplastic large cell lymphoma [ALCL] and angioimmunoblastic lymphoma [AITL] in second CR). In less favorable histologies, HDT seems to provide limited benefit, with the majority of patients experiencing post-transplant relapse. The use of autologous HCT to consolidate first remission has been evaluated in several prospective trials. Again, the best results were observed in ALCL, but the superiority of this approach over chemotherapy alone needs confirmation in randomized trials. In less favorable histologies, high-dose consolidation resulted in low survival rates comparable to those obtained with chemotherapy alone, and without randomized trials it is hard to recommend this strategy to all patients with newly diagnosed PT/NKCL. Allogeneic HCT might provide potent and potentially curative graft-vs-lymphoma effect and overcome chemotherapy resistance. Only a few studies have been reported to date on allogeneic HCT in PT/NKCL. Based on available data, eligible patients benefit significantly from this approach, with 50% or more patients achieving long-term disease control or cure, although at the expense of significant treatment related mortality (TRM). Reduced-intensity conditioning regimens appear to have lower TRM and might extend this approach to older patients. With the recent approval of several novel agents for relapsed/refractory PT/NKCL and their impact on survival of patients after relapse, it is becoming even more difficult to assess the benefit of HCT on overall survival and apply the results of non-randomized studies to clinical practice. Development of effective clinico-pathologic prognostic models might provide the opportunity to better define the role of HCT for patients with various subtypes of PT/NKCL. The first randomized trial comparing upfront autologous and allogeneic HCT was initiated by the German High-Grade Non-Hodgkin Lymphoma Study Group, and the results of this study might help answer some of the controversies for the first time.