Allogeneic Stem Cell Transplantation Using a Reduced Intensity Conditioning (RIC) Regimen Has the Capacity To Produce Durable Remissions and Long Term Disease-Free Survival in Patients with High Risk Acute Myeloid Leukemia (AML).

The toxicity of allogeneic stem cell transplantation (SCT) can be substantially reduced by the use of a reduced intensity conditioning (RIC) regimen and this has increased the proportion of patients with myeloid malignancies eligible for allogeneic transplantation. However, the capacity of RIC allografts to produce durable remissions in patients with AML and MDS has not yet been defined and consequently their role in the management of these diseases remains conjectural. Seventy-six patients with high risk AML or MDS were allografted using a fludarabine/melphalan RIC regimen incorporating alemtuzumab. The median age of the cohort was 52 years (range 18–71 years). There were 46 males and 30 females; 41 patients received an allograft from an unrelated donor and 35 from a matched sibling donor. The 100 day transplant related mortality was 9% and no patient developed greater than Grade 2 graft-versus-host disease (GVHD). With a median follow-up of 36 months (range 13–70 months) 27 patients were alive and in remission with a 3y actuarial overall survival (OS) and disease-free survival (DFS) rate of 41% and 37% respectively. The 3y OS and DFS of patients with AML in complete remission (CR) at the time of transplantation was 48% and 42% respectively. In a multivariate setting, Cox regression analysis demonstrated prognostic significance of disease stage at the time of transplant with improved DFS in patients with AML in CR at the time of transplantation (HR=2.03, 95% CI=1.02–4.07). Disease relapse was the commonest cause of treatment failure occurring at a median time of 6 months post-transplant. Fourteen out of 27 (52%) patients relapsed within 6 months and 23/27 (85%) within twelve months defining a relatively narrow window for therapeutic intervention to prevent disease recurrence. The extended follow-up in this series identifies a high risk of early disease relapse but provides evidence that RIC allografts are capable of producing sustained disease free survival in a significant number of patients with AML who would be ineligible for allogeneic transplantation using a myeloablative conditioning regimen.