Higher Leukemia Free Survival after Post-Induction Hematopoietic Cell Transplantation Compared to Consolidation Therapy in Patients >60 Years with Acute Myelogenous Leukemia (AML): Report from the AML 2004 East German Study Group (OSHO)

Treatment of elderly patients with AML remains challenging. While increasing doses of induction and consolidation chemotherapy have failed to improve outcome, efforts to decrease relapse rates using the graft-versus-leukemia effect have shown promising results in phase II studies. In the present analysis of the prospective OSHO 2004 study we evaluated the effect of post-induction hematopoietic cell transplantation (HCT) in comparison to conventional consolidation chemotherapy (CT) on outcome in elderly patients with AML.

The OSHO 2004 study is part of the German intergroup study. Upon achieving complete remission (CR) after induction, patients were assigned to CT or HCT depending on the availability of a matched related or unrelated donor. Unrelated, single antigen mismatched donors were accepted in high risk situations. By April 2014 from 817 eligible patients, 505 entered CR (62%) after one or two induction therapies. From the 452 patients who received consolidation in CR 1, 31 patients (7%) relapsed and 10 (2%) died of complications during consolidation. No further therapy for medical reasons was given to 73 patients, 206 patients received second consolidation with cytarabine (0.5 g/m² i.v. bid d1, 3, 5) plus mitoxantrone (10 mg/m² d1-2) and 132 patients underwent HCT. Most frequent conditioning regimens for HCT were low dose TBI (83%) and treosulfan/fludarabine (12%). Most of the patients received HCT from unrelated (80%) donors and the majority received grafts from HLA-identical (78%) donors. Our analysis was restricted to the 315 patients <75 years receiving either CT or HCT. Probabilities for overall survival (OS) and leukemia free survival (LFS) were estimated according to the Kaplan-Meier method and differences tested by the log-rank test. Relapse incidence (RI) and non relapse mortality (NRM) were described by estimating the cumulative incidence and testing the differences using the Gray's test. Multivariate Cox regression models and competing risks regression models were used to identify independent prognostic variables for outcomes.

The median age was 67 (60-74) and 65 (60-74) years in the CT and the HCT groups (p<0.0005), respectively. There were no differences between CT and HCT regarding gender, AML type (de novo, secondary or therapy related) and FLT3 mutation status. However more patients with mutated NPM1 were observed in the CT as compared to the HCT group (39% vs 28%; p=0.07) and more patients entered into remission after one induction in the CT as compared to the HCT group (89% vs. 81%; p=0.05). Low risk cytogenetics and normal karyotype were present more frequently in the CT than in the HCT arm (p<0.0005). The interval from CR to CT was 50 days and from CR to HCT 72 days (p<0.0005).

Patients receiving related or unrelated matched/mismatched HCT had superior LFS than those receiving CT (32±5% vs. 13±4% at 8 years, respectively; p<0.0005). The difference was more distinct when only those patients with matched related or unrelated donors were compared to those receiving CT (36±6% vs. 13±4% at 8 years; p<0.0005). Similar figures were obtained for overall survival [OS, 35±5% matched/mismatched HCT vs. 24±4% for CT (p=0.18) and 41±6% for matched HCT patients vs. 24±4% for CT (p=0.09)]. RI was lower after HCT (40±5%) than after CT (79±5%; p<0.0001). In contrast, NRM was higher in HCT patients (28±7%) than in CT patients (9±11%; p<0.0001).

Subpopulation analyses identified no difference in LFS and OS between matched related versus unrelated HCT. The difference in LFS between HCT and CT was highest in patients with normal karyotype, high risk cytogenetics and patients with non-monosomal karyotyp.

Prognostic factors for LFS, OS, RI and NRM were analyzed in a multivariate analysis. Significant prognostic factors for LFS were cytogenetic risk (p=0.04), HCT (p=0.01) and FLT3 mutation status (p=0.07). OS was determined by cytogenetics p<0.01) with a trend for lower age (p=0.07) and HCT (p=0.14). Prognostic factors for RI were cytogenetics (p< 0.0006), FLT3 mutation status (p<0.03) and HCT (p<0.0005). NRM was influenced by HCT (p=0.002).

Conclusions: HCT from related or unrelated donors improved LFS and OS in patients with AML over the age of 60 years and in particular in those with high risk cytogenetics or normal karyotype disease. The LFS of over 30% after 8 years achieved by HCT represents a marked improvement in the prognosis of patients with AML aged 60-75 years in CR1.