Session: 617. Acute Myeloid Leukemias: Biomarkers, Molecular Markers and Minimal Residual Disease in Diagnosis and Prognosis: Poster II
Hematology Disease Topics & Pathways:
Research, Translational Research, Minimal Residual Disease
Methods: Patients aged 18 or older who underwent alloHCT for AML in CR1 between 2013 and 2019 reported to have a FLT3-TKD variant at diagnosis and a pre-conditioning remission blood sample available in the CIBMTR biorepository were eligible for this study. Single-amplicon NGS (SA-NGS) library generation utilizing UMI-tagged primers targeting the D835 and I836 codons of FLT3 was performed on 400ng genomic DNA sequenced with unique dual indices, with error-corrected variant calling. Primary outcomes were overall survival (OS) and cumulative incidence of relapse (CIR). Secondary outcomes were relapse-free survival (RFS) and non-relapse mortality (NRM), with NRM being considered as a competing risk.
Results: A total of 351 patients met inclusion criteria for this study, and 342 (97.4%) had sufficient DNA for SA-NGS and were analyzed for clinical outcomes. Of these patients, 81 (23.7%) experienced relapse at a median of 5 months post-alloHCT. Using the current ELN-recommended variant allele fraction (VAF) threshold of 0.1% for NGS-based AML MRD, 14 patients (4.1%) tested positive. Patients with FLT3-TKD MRD VAF≥0.1% experienced higher rates of relapse (73.8% vs. 20.5%, p < 0.0001) and decreased OS (11.4% vs. 66.8%, p < 0.001) compared to VAF<0.1%.
The highly sensitive SA-NGS method allowed for exploration to determine if a deeper VAF threshold of 0.01% (previously validated for NPM1 and FLT3-ITD in the Pre-MEASURE study) was prognostic for FLT3-TKD as an MRD target. This led to an additional 20 patients being reclassified as positive (n = 34 with VAF above 0.01%, =9.9%). However, there was no significant difference in CIR (33.6% vs. 19.7%, p = 0.089) or OS (65.2% vs. 66.9%, p = 0.267) between patients with 0.01%≤VAF<0.1% and VAF<0.01% (Figure). Out of 28 SA-NGS positive calls, 6 could not be validated by orthogonal digital droplet PCR testing, and interestingly, none of those 6 patients experienced relapse.
Site-reported pre-transplant remission multiparametric flow cytometry (MFC) was available for 335 patients (98%). Results of MFC were not associated with differences in CIR (HR 1.2, 95% CI 0.52 – 2.76, p = 0.67) or OS (HR 0.78, 95% CI 0.34 – 1.77, p = 0.551). In multivariable analysis, FLT3-TKD NGS-MRD VAF≥0.1% remained prognostic for CIR (HR 6.1, 95% CI 3.1 – 12.0, p < 0.001) and OS (HR 3.2, 95% CI 1.7 – 5.9, p < 0.001).
Conclusions: Detectable persistence of FLT3-TKD variants in blood from AML patients in first remission prior to first alloHCT is rare, but at a VAF level of 0.1% was strongly associated with increased relapse and death after transplant compared to those testing negative. In contrast to FLT3-ITD NGS-MRD, no evidence was found to support lowering the NGS-MRD VAF threshold from 0.1% to 0.01% for FLT3-TKD. Alternative methodology may further improve NGS-MRD test performance. Site-reported MFC prior to alloHCT did not stratify for post-transplant relapse or survival. Optimal NGS-MRD testing for patients with AML will likely require a multi-target approach and testing for persistence of FLT3-TKD MRD is shown here to represent an important component of this strategy.
Disclosures: Andrew: Astra Zeneca: Current Employment. Auletta: National Marrow Donor Program: Current Employment; Takeda: Membership on an entity's Board of Directors or advisory committees; AscellaHealth: Membership on an entity's Board of Directors or advisory committees. El Chaer: Sanofi: Research Funding; PharmaEssentia: Research Funding; BioSight: 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; MorphoSys: Consultancy; Sumitomo Pharma Oncology: Consultancy, Research Funding; Fibrogen: Research Funding; Amgen: Consultancy, Research Funding; Bristol Myers Squib: Research Funding; Celgene: Research Funding. Corner: Bio-Rad Laboratories: Current Employment, Current holder of stock options in a privately-held company. Jimenez Jimenez: Abbvie: Research Funding. de Lima: AbbVie: Other: Data Safety Monitoring Board; Novartis: Other: Data Safety Monitoring Board; Miltenyi Biotec: Research Funding; 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. Kebriaei: Pfizer: Consultancy, Honoraria; Jazz: Consultancy, Honoraria. Hourigan: Foundation of the NIH AML MRD Biomarkers Consortium: Research Funding.