Favorable Outcome of Older Patients with AML and a Favorable Genotype NPM1mut FLT3-ITD Treated with Intensive Chemotherapy: A Subgroup Analysis of Cetlam Protocol 2003 & 2012

Introduction

Younger patients with acute myeloid leukemia and intermediate cytogenetic risk (AML-IR) harboring NPM1 mutation (NPM1mut) without FLT3 internal tandem duplication (FLT3-ITD) have a relatively favorable prognosis, and are not deemed as candidates to receive an allogeneic hematopoietic stem cell transplantation in first complete remission (CR1). However, it remains uncertain if this favorable prognosis is also maintained in older patients within the same molecular features with some conflicting results.

Patients and methods

We analyzed the cohort of patients ≥60 year-old considered fit for intensive chemotherapy and included in the CETLAM protocols LMA-2003 and LMA-2012 for patients up to 70, consisting of a standard induction chemotherapy, HiDAC post-remission therapy, followed by alloHSCT in selected patients with high-risk features. Overall we identified 192 patients between 60 and 71 year-old diagnosed with AML-IR with known NPM1 and FLT3 mutational status.

Results

We identified 192 AML-IR patients (93♀, 99♂) aged >=60 (median age was 65 years old (range: 60-71)), with a median WBC count 10.6 x 10⁹/L (range: 0.23-400 x 10⁹/L), median bone marrow blasts 65% (range: 20-100%). Overall, CR rate was 78%, five-year overall survival (OS) was 30±4%, and leukemia-free survival (LFS) was 31±4%. Patients were classified in three molecular groups depending on NPM1mut and FLT3-ITD: 40 patients harbored NPM1mut/FLT3 without ITD (FAV group), 98 patients had NPM1wt/FLT3wt, and 54 had a FLT3-ITD. Five-year OS of these 3 groups were: 64±9%, 25±6%, and 19±6%, respectively (p<0.001). Since the two latter groups, NPM1wt/FLT3wt and FLT3-ITD, did not show significant differences, we decided to group them in a sole subgroup (UNFAV group). There were no differences in the complete remission rate between patients of FAV and UNFAV groups (88% vs 78%, p=ns), but the cumulative incidence of relapse was significantly higher for patients of the UNFAV group (54 vs. 17.5%, p=0.000654).

Multivariate analysis for OS, including WBC count, bone marrow blasts and molecular group (NPM1mut/FLT3wt vs. the other groups) identified WBC and molecular subgroup showed significance for the WBC count (HR=1.003, 95% CI: 1-1.006) and the molecular group (FAV vs. UNFAV, HR=0.345, 95% CI: 0.192-0.621).

Interestingly, when we compared the outcome of the FAV group with a cohort of younger patients (up to 60, n=99) with the same molecular features included in these 2 protocols, the outcome did not differ depending on age (5-year OS 69±5% for younger patients, and 64±9% for older patients, p=0.463, and 5-yr LFS 67±5% for younger patients, and 55±12% for older patients, p=0.567). Moreover, the outcome of a small cohort of FAV patients older than 65 years (n=16) included in these protocols was relatively favourable, with a 5-yr OS and LFS not differing substantially from that of younger patients allocated in the same molecular subgroup.

Conclusions

The favorable impact of NPM1mut/FLT3-ITDneg genotype was maintained in a cohort of patients >60 who received intensive chemotherapy, with a high proportion of long-standing responses after HiDAC-based post-remission therapy.