Allogeneic Stem Cell Transplantation for Elderly Patients with Intermediate-Risk Cytogenetic Acute Myeloid Leukemia and Internal Tandem Duplication of FLT3 (FLT3-ITD); A Study from the Acute Leukemia Working Party (ALWP) of the European Society of Blood and Marrow Transplantation (EBMT)

Introduction: The presence of an internal tandem duplication of FLT3 (FLT3-ITD) confers a higher risk of relapse and is now a current indication of allogeneic stem cell transplantation (SCT) in patients with intermediate-risk cytogenetic acute myeloid leukemia (IRC-AML) in first complete remission (CR1). Most studies encouraging this strategy have been performed in patients below 60 year-old, after a myeloablative conditioning (MAC) and using a sibling donor. Because age remains associated with a worse outcome after SCT, we decided to analyse outcomes of SCT in patients aged 60 year-old or older with intermediate-risk AML and FLT3-ITD.

Methods: Using the EBMT registry, we selected de novo acute myeloid leukemia (AML) harboring IRC-AML and FLT3-ITD in patients transplanted from a related or matched unrelated donor (9/10 or 10/10) between January 2000 and July 2014.

Results: Two hundred and five patients have been allocated. Median age at the time of SCT was 64 (range, 60-75) year-old and median follow-up was 20 (range, 2-139) months. Ninety-four percent of the patients had a good performance status (Karnofsky at SCT ≥ 80%). Most patients had a normal karyotype at diagnosis (90% versus 10% with other intermediate-risk karyotype) and NPM1 status was reported in 131 patients out of which 100 (76%) were mutated. Thirty-four patients received a MAC, 142 had a reduced-intensity conditioning (RIC) and 29 a non-myeloablative conditioning (NMA). One hundred forty-six patients received their SCT in first remission (CR1), 24 in second remission (CR2) and 35 in more advanced stage of the disease, respectively. The 2-year leukemia-free survival (LFS) was 52% in patients in CR1, 17% in those in CR2 and 11% in patients with advanced disease, respectively (p<0.005). Similarly, the 2-year overall survival (OS) was 54% in CR1, 24% in CR2 and 11% in advanced disease, respectively (p<0.005). The 2-year non-relapse mortality (NRM) for the all cohort was 20%. The cumulative incidence of grade II to IV acute graft-versus-host disease (GvHD) was 24% and that of chronic GvHD was 30%.

In multivariate analysis, disease status at SCT was the most powerful predictor of worse LFS and OS. Age, as a continuous variable, was not significantly associated with outcomes. Donor type (unrelated versus sibling donor) and donor CMV positivity correlated with worse OS and higher NRM. Next, we performed a second analysis focusing on patients transplanted in CR1. A multivariate analysis performed in this subgroup showed that age, as a continuous variable, did not translate into worse LFS, OS or NRM.  Interval from diagnosis to CR1 was significantly associated with LFS, being 63% in patients achieving CR1 in less than 43 days and 45% in patients achieving CR1 in more than 43 days, respectively (p<0.005). NMA conditioning was associated with a trend to a worse OS.

Conclusion: Allogeneic SCT in elderly (≥60 up to 75 year-old) patients with IRC-AML harboring the FLT3-ITD mutation, similar to current strategy in younger patients, appears as a good treatment strategy if performed in CR1, independently of age, with somewhat inferior outcome in transplants from unrelated donors. Nevertheless, indication for transplantation should still be evaluated taking into account donor type, co-morbidities and performance status.