Prognostic significance of FLT3-ITD length in AML patients treated with intensive regimens

Abstract

FLT3-ITD mutations are detected in approximately 25% of newly diagnosed adult acute myeloid leukemia (AML) patients and confer an adverse prognosis. The FLT3-ITD allelic ratio has clear prognostic value. Nevertheless, there are numerous manuscripts with contradictory results regarding the prognostic relevance of the length and insertion site (IS) of the FLT3-ITD fragment. We aimed to assess the prognostic impact of these variables on the complete remission (CR) rates, overall survival (OS) and relapse-free survival (RFS) of AML patients with FLT3-ITDmutations. We studied the FLT3-ITD length of 362 adult AML patients included in the PETHEMA AML registry. We tried to validate the thresholds of ITD length previously published (i.e., 39 bp and 70 bp) in intensively treated AML patients (n = 161). We also analyzed the mutational profile of 118 FLT3-ITD AML patients with an NGS panel of 39 genes and correlated mutational status with the length and IS of ITD. The AUC of the ROC curve of the ITD length for OS prediction was 0.504, and no differences were found when applying any of the thresholds for OS, RFS or CR rate. Only four out of 106 patients had ITD IS in the TKD1 domain. Our results, alongside previous publications, confirm that FLT3-ITD length lacks prognostic value and clinical applicability.

Figure 1

Clinical outcome stratified according to the FLT3-ITD length (cutoff 39 bp) for all patients treated with intensive chemotherapy. (A) Overall survival. (B) Relapse-free survival. (C) OS according to the FLT3-ITD length and allelic ratio. (D) OS according to the FLT3-ITD length and 2010 ELN genetic risk. AR,allelic ratio.

Figure 2

Clinical outcome stratified according to the FLT3-ITD length (cutoff 70 bp) for all patients treated with intensive chemotherapy. (A) Overall survival. (B) Relapse-free survival. (C) OS according to the FLT3-ITD length and allelic ratio. (D) OS according to the FLT3-ITD length and 2010 ELN genetic risk. AR, allelic ratio.

Figure 3

Analysis of FLT3-ITD insertion sites from 106 FLT3-ITD-positive AML patients. In our cohort, FLT3-ITD was located in the JMD domain (JMD-B, JMD-S, JMD-Z and HR) in 98 patients and in the TKD1 domain (B1, NBL and B2) in four patients. A detailed analysis of all patients showed ITD integrations in the JMD-B, amino acids 572 to 578, in six patients; the JMD-S, amino acids 579 to 592, in 42 patients; the JMD-Z, amino acids 593 to 603, in 43 patients; the HR, amino acids 604 to 609, in seven patients; the B1 of TKD1, amino acids 610 to 615, in one patient; the NBL, amino acids 616 to 623, in two patients; and the B2, amino acids 624 to 630, in one patient. TM,transmembrane domain; JMD, juxtamembrane domain; JMD-B, binding motif; JMD-S, switch motif; JMD-Z, zipper motif; HR, hinge region; TKD1, tyrosine kinase domain 1; B1, beta1-sheet; NBL, nucleotide binding loop; B2, beta2-sheet; and TKD2, tyrosine kinase domain 2.

Figure 4

The landscape of mutations identified by NGS in AML patients. These mutations arearranged in increasing order by FLT3-ITD length. Green indicates non-mutated genes, red indicates mutated genes and white indicates non-mutated genes. * Genes with a P value < 0.05 in the Mann–Whitney test correlating mutational status with ITD length.

Figure 5

Flow diagram showing all AML patients with FLT3-ITD mutations in the study period between 2003 and 2019 on the basis of genetic data and treatment administered. NGS, next-generation sequencing.