Allogeneic Stem Cell Transplantation Provides Durable Remission in Patients with Primary Mediastinal Large B Cell Lymphoma

Standard therapy for relapsed or refractory (rel/ref) primary mediastinal large B cell lymphoma (PMBCL) is salvage therapy followed by autologous (auto) hematopoietic stem cell transplantation (HSCT). However, many patients have refractory disease and are unable to undergo autoHSCT, and a sizeable proportion of patients will relapse after autoHSCT. By analogy to diffuse large B cell lymphoma, these patients may be treated with allogeneic (allo) HSCT with curative intent, but at the risk of significant morbidity and mortality. Given the advent of effective immunotherapy approaches for rel/ref PMBCL, it is important to better understand the toxicity and efficacy of alloHSCT in these patients, to which these new approaches could be an alternative. Therefore, we retrospectively studied the outcomes of alloHSCT in a multicenter cohort of 28 patients with rel/ref PMBCL who underwent transplantation at 4 centers. Most patients (79%) were sensitive to pretransplantation therapy and 86% received reduced-intensity conditioning. The overall progression-free survival (PFS), overall survival (OS), and cumulative incidences of nonrelapse mortality and relapse in the cohort at 5 years were 34%, 45%, 32%, and 33%, respectively. Outcomes were significantly better in patients with pretransplantation responsive disease (2-year PFS and OS of 50% and 58%, respectively) compared with refractory patients (2-year PFS and OS of 0%). In our multicenter retrospective study, alloHSCT produced durable remissions in a proportion of patients with treatment-sensitive disease before transplantation (5-year PFS of 44%) and should be considered in the treatment of patients with rel/ref PMBCL.