Long-Term Outcome of Peripheral Blood Autologous Stem Cell Transplantation (AutoSCT) for De Novo Acute Myeloid Leukemia in Patients Achieving First Complete Remission after One Vs Two Induction Courses: A Study from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation (EBMT)

Background: Achieving a first complete remission (CR1) is the primary goal in the treatment of AML and is an important prognostic factor for transplantation outcome in general and even more so for autologous transplantation (AutoSCT). However, there are no data for AutoSCT indicating whether the number of chemotherapy courses (1 vs 2) needed to achieve CR1 is of prognostic significance for transplantation outcome.

Methods: Using the EBMT/ALWP registry, we compared transplantation outcomes of adult patients (pts) aged ≥18 years with de novo AML that underwent a peripheral blood AutoSCT in 2000-2019 in CR1 achieved following one vs two chemotherapy courses. The primary outcome was the Leukemia Free Survival (LFS). Multivariate analysis (MVA) adjusting for differences between the groups and knowns factors were performed using Cox's proportional- hazards regression model for outcomes.

Results: 1825 pts were included: 1532 (84%) with one and 293 (16%) with two induction chemotherapies courses. Time from diagnosis to AutoSCT was 4.7 (3.9-5.8) vs 5.7 (4.7-7.1) months, respectively (p<0.001). Median follow-up was 7.9 (95% CI: 7.4-8.4) and 7.7 (95% CI: 7.0-8.6) years, respectively (p=0.8). Median year of transplant was 2005 (2002-2009) and 2004 (2002-2007), respectively (p<0.001). Median age was 49 (38-57) and 47 (36 -56) years (p=0.06); 54% and 57 % of both groups were male, (p=0.35). Cytogenetic risk as defined by the Medical Research Council (MRC) classification, differed significantly between the two induction groups (p<0.001). Patients with one induction had a higher percentage of favorable-risk than those with two inductions (18% vs 14%), and a lower percentage of adverse-risk cytogenetics (6% vs 13%), while 76% and 73%, respectively, had intermediate-risk cytogenetics (missing data-11percentage). Karnofsky performance score (KPS) > 90 was higher in pts receiving 1 vs 2 inductions, 71% and 58% of pts, respectively (p<0.001). The most frequent conditioning regimen for both groups was Busulfan (Bu) /Cytoxan (Cy) 50% vs 45% and Bu / Melphalan (Mel) 17% and 19%, respectively, for induction groups 1 and 2, respectively.

Day 30 neutrophil engraftment incidence was 96% and 96.5%.

Five -year non-relapse mortality (NRM) was 6.2% vs 6.0% for pts achieving CR1 with 2 vs 1 chemotherapy courses, respectively, and did not differ significantly (HR=1.31 (95% CI: 0.81-2.10), p=0.27). Five -year relapse incidence (RI) was higher :67.2% vs 52.3%, (HR=1.46 (95% CI: 1.25-1.72), p<0.001), while LFS and overall survival (OS) were lower for pts achieving CR1 with 2 vs 1 course of chemotherapy: 26.6% vs 41.7% (HR= 1.42 (95% CI: 1.22-1.66), p<0.001) and 36.2% vs 53.3%, (HR=1.48 (95% CI: 1.25-1.75), p<0.001), respectively (Figure). Other significant prognostic factors in MVA were adverse- compared to good risk cytogenetics and older age (per 10 years) for all AutoSCT outcome parameters including RI, NRM, LFS and OS; intermediate compared to good risk cytogenetics for RI, LFS and OS; female gender for RI and LFS ;and year of transplant for RI and OS.

Conclusions: The five -year RI was higher and transplantation outcomes significantly inferior in pts with AML undergoing AutoSCT but who received two lines of chemotherapy to achieve CR1. Such pts may benefit from additional novel therapies in the conditioning or post-AutoSCT or be considered for allogeneic transplantation in an attempt to reduce their high RI and improve outcomes.

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