The outcome of patients with therapy-related myelodysplasia (t-MDS) or t-AML is very poor. The only curative treatment option implements allogeneic hematopoietic cell transplantation (aHCT); however, long-term follow-up data beyond 5 years are scarce. Here we report on a cohort of 79 consecutive patients with a median age of 58 years (range (r): 20-76) at transplantation and a median follow-up of 7.5 years (r: 0.07-19.0). Only 19 (24.1%) patients were in CR before aHCT. Non-relapse mortality and relapse rates were 23% (95% confidence interval, 15-35%) and 42% (32-55%) at 5 years, and 32% (22-46%) and 44% (34-57%) at 10 years, respectively. Disease-free survival (DFS) and overall survival (OS) rates were 35% (24-46%) and 38% (27-49%) at 5 years, and 24% (14-36%) and 24% (13-36%) at 10 years, respectively. Although cytogenetic aberrations were associated with shorter DFS and higher relapse risk, persistent disease at the time of transplantation, an unrelated donor and patient age were not associated with shorter OS. In conclusion, long-term survival beyond 10 years of t-MDS/t-AML patients after aHCT is possible, even for refractory patients. Therefore, early donor search and rapid transplantation are warranted, also to decrease the risk of disease-related deterioration of patients' performance status.Bone Marrow Transplantation (2016) 51, 771-777; doi:10.1038/bmt.2015.338; published online 11 January 2016 INTRODUCTION Cytotoxic agents, especially alkylating and topoisomerase II targeting drugs, as well as ionizing radiotherapy in the successful treatment of most cancer types and to some extent also in nonmalignant diseases, bear a significant long-term risk of developing therapy-related malignancies such as myelodysplasia (t-MDS) and t-AML. 1,2 Despite intensive efforts to reduce the risk of developing t-MDS/t-AML by using fewer cycles of dose-intense chemotherapy for a given primary disease and thus to decrease cumulative doses, this late occurring side effect remains a challenging clinical problem. 3 Treatment of t-MDS/t-AML, which often occurs with other comorbidities, is complex and the outcome of patients treated with low-or even high-dose chemotherapy alone remains poor. Beyond other factors, this is especially attributed to older age, therapy resistance and cytogenetic abnormalities including monosomies or complex karyotypes. 4,5 In recent years, it has become evident that the most successful curative treatment concept for t-MDS/t-AML patients resulting in substantial remission rates implements allogeneic hematopoietic cell transplantation (aHCT). Using a myeloablative conditioning regimen in 77% of patients in a cohort of 868 patients with a median age of 40 years, Litzow et al. 6 reported an overall survival (OS) rate of 22% (95% confidence interval (CI), 19-26%) after 5 years, although the non-relapse mortality (NRM) and relapse rate at that time were 48% (95% CI, 44-51%) and 31% (95% CI, 28-34%), respectively. In another study from the European Group for Blood and Marrow Transplantation, Kröger et al. 7...