EHA Library - The official digital education library of European Hematology Association (EHA)

Abstract: EP376

Type: E-Poster Presentation

Session title: Acute myeloid leukemia - Biology & Translational Research

Background

FLT3-ITD occurring in ~25% of adult AML patients (pts) is associated with poor prognosis. FLT3-ITD represents an attractive target for MRD monitoring particularly in pts treated with a tyrosine kinase inhibitor. We have recently demonstrated that NGS can overcome the limitations of the broad heterogeneity of ITD length and insertion site (IS) offering the opportunity for MRD monitoring in FLT3-ITD⁺ AML.

Aims

To validate our NGS-based FLT3-ITD MRD assay and to evaluate the prognostic impact of FLT3-ITD MRD monitoring in FLT3-ITD⁺ AML treated within the AMLSG16-10 trial (NCT01477606) combining intensive chemotherapy with midostaurin followed by midostaurin maintenance.

Methods

Using FLT3-ITD paired-end NGS (Illumina MiSeq) and getITD with a variant allele frequency (VAF) sensitivity of 10^-4-10^-5, 336 bone marrow (BM) and 36 peripheral blood samples from 96 FLT3-ITD⁺ AML pts were analyzed at diagnosis (Dx), after two cycles of chemotherapy (Cy2), at end of treatment (EOT), and during 3-12 months follow-up (FU). All pts achieved complete remission (CR) after Cy2. Allogeneic hematopoietic cell transplantation in first CR (HCT in CR1) was performed in 72 (75%) pts. NPM1 and DNMT3A mutation status were available for all pts (NPM1^mut, n=74; DNMT3A^mut, n=48; NPM1^mut/DNMT3A^mut, n=46); NPM1^mut MRD data in 67 pts.

Results

At Dx we identified 296 ITDs; with 71% of the pts exhibiting >1 ITD at Dx (median 2; range, 1-15). Median length was 48 nucleotides (range, 9-240) and median VAF 0.280% (0.006-90.21). Of the 296 ITDs, 69% located in the juxtamembrane domain and 31% in the tyrosine kinase domain-1. VAF did not correlate with length or IS, whereas ITD length correlated with IS: the more 3´ the IS, the longer the ITD (Rho=0.51; p<.001). Median total ITD VAF per pt was 32.6% (0.57-90.21) and correlated positively with white blood cell count (WBC, Rho=0.233; p=.024), and inversely with ITD number (Rho=-0.221; p=.03). There were no correlations with other clinical or genetic features.

Pts’ total ITD VAF significantly decreased after Cy2 and at EOT (median log₁₀ reduction: 4.4 and 4.7; p<.001, each), and MRD negativity (MRD^-) was achieved in 64% and 87%, respectively. Concurrent NPM1^mut favorably impacted on log₁₀ VAF reduction (median, 4.7 for NPM1^mut vs 4.7 for DNMT3A^mut/NPM1^mut vs 2.9 others; p<.001) and MRD^- (78 vs 72 vs 30%; p=.001) after Cy2, but exerted no impact at EOT. NPM1^mut and FLT3-ITD MRD course correlated positively after Cy2 (Rho=0.423; p=.001), but not at EOT, likely due to the higher sensitivity of the NPM1^mut MRD assay (qRT-PCR).

Median follow-up was 3.8 years (95% CI, 3.0-4.7). Survival analyses for cumulative incidence of relapse (CIR) and overall survival (OS) revealed in strong trend lower CIR for total VAF per pt at Dx >32.6% (p=.055), significantly lower CIR for VAF reduction >4.4 log₁₀ (MR^4.4) after Cy2 (p=.028), MR^4.7 at EOT (p=.007), and for MRD^- at EOT (p<.001). There was no impact on OS. In exploratory Cox regression (n=72), including BM blasts, WBC, lactate dehydrogenase, age, NPM1^mut, and HCT in CR1 as time dependent variable, MRD^- at EOT was the only consistent favorable variable for CIR (HR, 0.1; p=.001) and OS (HR, 0.33; p=.046). NPM1^mut (HR, 0.04; p<.001) and HCT in CR1 (HR, 0.1; p=.002) were favorable for CIR.

Conclusion

In this cohort of FLT3-ITD⁺ AML treated with intensive chemotherapy and midostaurin we could demonstrate that a large proportion of pts became MRD^- at EOT by FLT3-ITD NGS-based MRD monitoring which reveals as a promising tool to monitor therapy response and to identify pts at a higher risk of relapse.

Keyword(s): Acute myeloid leukemia, Flt3-ITD, Minimal residual disease (MRD)