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4325 Measurable Residual FLT3-ITD before Allogeneic Transplant for Acute Myeloid LeukemiaClinically Relevant Abstract

Program: Oral and Poster Abstracts
Session: 617. Acute Myeloid Leukemias: Biomarkers, Molecular Markers and Minimal Residual Disease in Diagnosis and Prognosis: Poster III
Hematology Disease Topics & Pathways:
Research, Translational Research, Minimal Residual Disease
Monday, December 11, 2023, 6:00 PM-8:00 PM

Laura W Dillon, PhD1*, Gege Gui, ScM1, Niveditha Ravindra, MD1*, Georgia Andrew, BSc1*, Devdeep Mukherjee, PhD1*, Zoe Wong, BS1*, Ying Huang, PhD2*, Jason Gerhold2*, Matthew Holman, BSc2*, Jeffrey E Miller, PhD2*, Jeffery J. Auletta, MD3,4, Firas El Chaer, MD5, Steven M. Devine, MD3, Antonio M. Jimenez Jimenez, MD, MSc6*, Marcos de Lima, MD7*, Mark R. Litzow, MD8, Partow Kebriaei, MD9, Wael Saber, MD, MS10,11*, Stephen R. Spellman, MBS3,11*, Kristin M. Page, MD3,10 and Christopher S. Hourigan, DM, DPhil1,12

1Laboratory of Myeloid Malignancies, Hematology Branch, National Heart, Lung, and Blood Institute, Bethesda, MD
2Invivoscribe, Inc., San Diego, CA
3Center for International Blood and Marrow Transplant Research, Minneapolis, MN
4Hematology/Oncology/Bone Marrow Transplant and Infectious Diseases, Nationwide Children's Hospital, Columbus, OH
5Department of Medicine, Division of Hematology and Oncology, University of Virginia Comprehensive Cancer Center, Charlottesville, VA
6Sylvester Comprehensive Cancer Center, Miller School of Medicine, Miami, FL
7Division of Hematology, The Ohio State University Wexner Medical Center, Columbus, OH
8Division of Hematology, Mayo Clinic, Rochester, MN
9Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas MD Anderson Cancer Center, Houston, TX
10Medical College of Wisconsin, Milwaukee, WI
11National Marrow Donor Program, Minneapolis, MN
12Myeloid Malignancies Program, National Institutes of Health, Bethesda, MD

Background: In the past year, multiple studies have demonstrated the drastically increased risk of relapse and death in patients with Acute Myeloid Leukemia (AML) who have persistent FLT3 internal tandem duplication (ITD) mutations detectable in clinical remission by next generation sequencing (NGS). Translating this evidence into a change in clinical practice requires both widely available testing and a clear understanding of the clinical implications of FLT3-ITD detection at defined threshold levels. In the largest of the recent studies (Pre-MEASURE, PMID: 36881031), we performed FLT3-ITD MRD detection in blood DNA collected from 608 patients at the time of first remission (CR1) prior to allogeneic hematopoietic cell transplant (alloHCT). To evaluate cross-assay comparability and the impact of residual disease burden levels, we performed analysis on this cohort using a commercially available FLT3-ITD MRD NGS assay.

Methods: Of the 608 patients aged 18 or older from the Pre-MEASURE study who received an alloHCT for FLT3-ITD mutated AML during CR1 at a CIBMTR reporting site in the USA between the years of 2013-2019, patients not experiencing non-relapse mortality and with sufficient DNA from pretransplant blood available were included in this analysis. A commercially available testing kit (IVS, Invivoscribe, San Diego, CA), which can detect FLT3-ITD MRD by NGS for up to 21 patients on one Illumina MiSeq flow cell, was used to establish a workflow following clinical testing standards and validated to detect ITDs down to a variant allele fraction (VAF) of at least 0.005%. Results were compared to those previously reported using an anchored multiplex PCR-based (AMP) targeted NGS assay. Overall survival (OS) and cumulative incidence of relapse were estimated with the day of transplant as time 0 using Kaplan-Meier estimation (log-rank tests) and Cox proportional hazards models.

Results: A total of 451 patients were included in this study, of which 173 (38%) experienced relapse (median: 5.2 months; range 0.7-52.1) and 133 (29%) died (median: 10.7 months; range 2-53.8) post-alloHCT. The IVS assay identified 232 FLT3-ITD variants with a median VAF of 0.005% (range 0.0002-44%) and length of 51bp (range 5-228). IVS positive patients had a median of 1 FLT3-ITD variant (range 1-15) and median maximum VAF of 0.01% (range 0.0003-44%).

Utilizing the same VAF cutoff of 0.01% for MRD positivity for the IVS test as used in the Pre-MEASURE study, patients testing positive prior to alloHCT exhibited higher rates of relapse (79% vs 31%, p<0.0001) and decreased survival (29% vs 77%, p<0.0001) at 3 years compared to testing negative. These results closely align with those previously reported using the AMP assay (Figure A).

The IVS test has a superior limit of detection compared with the AMP test, allowing investigation of alternative VAF thresholds. In total, 151 patients (33.5%) were FLT3-ITD MRD positive by IVS of which only 75 (17%) had VAF 0.01%. A threshold-free approach for the IVS test improved the ability to identify patients at risk of relapse, predicting 63% of relapses within 6 months of transplant compared to 43% with the 0.01% cutoff, but resulted in decreased specificity as 42% of all positive patients relapsed within 6 months vs. 57% with the 0.01% VAF cutoff.

In multivariable analysis, IVS FLT3-ITD MRD status was associated with both relapse and overall survival (Figure B). Additionally, stratifying patients by their level of residual FLT3-ITD disease burden prior to alloHCT revealed a dose-dependent increase in risk for death (Figure B) and relapse. Any detectable level of residual FLT3-ITD over 0.001% VAF exhibited increased risk, with VAFs 0.01% being the highest.

Conclusions: In this analysis of patients with AML from the Pre-MEASURE study, we show cross-assay evidence that the detection of residual FLT3-ITD variants in pre-transplant blood during CR1 is associated with significantly increased risk of relapse and death after alloHCT. The highly sensitive assay used in this study could identify ~2/3 of patients who relapsed within 6 months and demonstrated that a dose-dependent correlation between residual FLT3-ITD level and adverse clinical outcomes exists, with VAF 0.01% representing the highest risk. This evidence provides strong justification for NGS-based AML MRD clinical testing for persistent FLT3-ITD prior to alloHCT to identify patients at high risk of post-transplant relapse and death.

Disclosures: Andrew: Astra Zeneca: Current Employment. Huang: Invivoscribe, Inc: Current Employment, Current holder of stock options in a privately-held company. Gerhold: Invivoscribe, Inc: Current Employment. Holman: Invivoscribe, Inc: Current Employment. Miller: Invivoscribe, Inc: Current Employment, Current equity holder in private company, Current holder of stock options in a privately-held company. Auletta: Takeda: Membership on an entity's Board of Directors or advisory committees; National Marrow Donor Program: Current Employment; AscellaHealth: Membership on an entity's Board of Directors or advisory committees. El Chaer: BioSight: Research Funding; PharmaEssentia: Research Funding; Sanofi: Research Funding; Sumitomo Pharma Oncology: Consultancy, Research Funding; Fibrogen: Research Funding; MEI Pharma: Research Funding; Novartis: Research Funding; Arog Pharmaceuticals: Research Funding; Association of Community Cancer Centers: Consultancy; DAVA Oncology: Other: Travel grant; CTI Biopharma: Consultancy; AbbVie: Consultancy; Amgen: Consultancy, Research Funding; Bristol Myers Squib: Research Funding; Celgene: Research Funding; MorphoSys: Consultancy. Jimenez Jimenez: Abbvie: Research Funding. de Lima: Bristol Myers Scribb: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Data Safety Monitoring Board; AbbVie: Other: Data Safety Monitoring Board; Miltenyi Biotec: Research Funding. Kebriaei: Pfizer: Consultancy, Honoraria; Jazz: Consultancy, Honoraria. Hourigan: Foundation of the NIH AML MRD Biomarkers Consortium: Research Funding.

*signifies non-member of ASH