Factors Predicting Long Term Survival after Reduced Intensity Allogeneic Stem Cell Transplantation in Acute Myeloid Leukemia.

Allogeneic stem cell transplantation (SCT) performed using a reduced intensity conditioning (RIC) regimen represents an important new treatment modality in older patients with high risk acute myeloid leukaemia (AML) whose outlook with conventional chemotherapy would be poor. However assessment of its role has been hampered by the absence of long term follow-up data. Furthermore factors determining survival after RIC SCT have not been rigorously defined. In order to examine the anti-leukemic activity of RIC allografts in more detail we have examined the outcome of 170 patients with AML transplanted using a uniform conditioning regimen over a ten year period. Long term follow-up data (maximum 119 months) was collected on patients transplanted using a conditioning regimen consisting of fludarabine (30 mg/m² x 5 days), melphalan 140 mg/m² x 1 day and alemtuzemab (10 mg x 5 days). The median age of transplanted patients was 54 years (range 18–71). 88 patients were in CR1 at the time of transplant, 63 CR2/3 and 19 had relapsed or refractory disease. Cytogenetic information was available on 149 patients and of these 33 patients had adverse risk and 116 intermediate risk cytogenetics by MRC criteria. 83 transplants were performed using an HLA identical sibling donor and 87 using a volunteer unrelated donor. The 100 day transplant related mortality was 9%. 29% of patients developed Grade II-IV acute GVHD and 22% chronic GVHD. The 3 year overall survival (OS) for the whole group was 48% and 3 year disease free survival (DFS) 45%. 20 patients remain in remission more than five years post-transplant. Survival was significantly influenced by status at transplant (p=0.01), patient age (p= 0.01) and presentation cytogenetics (p=0.05) as determined by multivariate Cox proportional hazards regression. The 3 yr OS for patients transplanted in CR1 or CR2 was 51% and 52% respectively compared to 13% for patients with relapsed/refractory disease. Three year OS for patients with intermediate risk cytogenetics was 52% compared with 34% for adverse risk patients. Three year OS for patients under 60 years was 51% compared with 36% for older patients. This study demonstrates the ability of RIC allografts to deliver encouraging long term disease free survival rates in high risk AML. Pre-transplant characteristics can be used to predict outcome after a RIC allograft and older patients with active disease at the time of transplant or adverse cytogenetics require novel strategies in order to improve long term survival.