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Monitoring of NPM1 mutant (NPM1mut) measurable residual disease (MRD) in acute myeloid leukemia (AML) has an established role in patients who are treated with intensive chemotherapy. The European LeukemiaNet has defined molecular persistence at low copy number (MP-LCN) as an MRD transcript level

Introduction Molecular MRD assays targeting NPM1 mutant (mut) transcripts have an established role for monitoring treatment efficacy in patients with NPM1mut AML. Approximately 25% of NPM1mut patients show persistent MRD level in the bone marrow (BM) at the end of treatment (EOT), which is associated with a higher risk of relapse (Ivey, NEJM 2016; Kronke, JCO 2011). Molecular persistence at low copy number (MP-LCN) is defined by the European LeukemiaNet (ELN) as MRD positivity in patients in morphological complete remission (CR) with Methods Consecutive patients with newly diagnosed NPM1mut AML receiving at least 2 cycles of intensive chemotherapy were included if MRD remained detectable at EOT. UK patients were all enrolled in the NCRI AML17 and AML19 studies. Australian patients were retrospectively identified. BM samples were analyzed by either RT-qPCR (n=75) (Ivey, NEJM 2016) or ultra-deep next-generation sequencing (UD-NGS, n=5, excluded from Cox model). We applied the ELN definitions for molecular progression or relapse (considered together as molecular failure [MF]), MP-LCN and complete molecular remission (CRMRD-). Kaplan Meier survival estimates were calculated from EOT to death (OS), and/or morphologic relapse (RFS), and/or MF (EFS). The optimal NPM1mut expression threshold was pre-determined by recursive partitioning. Variables with p Results A total of 80 patients had NPM1mut detectable at a median of 37 days (range 19-90; 12 [15%] were >60 days) from last course of chemotherapy; characteristics summarized in Table 1. The majority of patients (89%) had received 3-4 cycles of chemotherapy. At EOT, the median NPM1mut transcript level by RT-qPCR was 11 copies (range 0.3-8699; 3 were >2000) and median reduction from baseline was 4.7 log (range 2.1-6.0). A total of 34 patients (45%; 4 not monitored) fulfilled the criteria for MP-LCN. With a median follow-up time of 24 mo (range 8-77), 27 (34%) spontaneously achieved a sustained CRMRD- for >6 months, 31 (39%) had MF and 13 (16%) had morphologic relapse without preceding MF (due to rapid relapse [n=8], lack of monitoring [n=3], extramedullary or NPM1 wild-type relapse [n=1 each]) (Figure 1). Nine patients (11%) had persisting MP-LCN (included transient MRD negativity): median interval between EOT to the last known positive sample was 12 mo (range 3-32), and all patients currently remain alive and without morphologic relapse by the data cut-off date July 13, 2020. Next, we examined the variables associated with MF and/or morphologic relapse. In univariate analysis, factors associated (p Conclusions We describe the natural history of patients with NPM1 mutated AML who remain MRD positive after completing intensive chemotherapy. Almost half either spontaneously achieve MRD-negativity or have stable low-level expression without relapse with minimum follow up of 8 mo. Patients with both FLT3-ITD and Disclosures Tiong: Pfizer: Consultancy; Servier: Consultancy; Amgen: Consultancy, Honoraria. Dillon:Abbvie: Honoraria, Research Funding; Novartis: Honoraria; Menarini: Honoraria; Astellas: Honoraria; Pfizer: Honoraria, Research Funding; Jazz Pharmaceuticals: Honoraria; Amgen: Honoraria, Research Funding. Bajel:Abbvie: Honoraria; Pfizer: Honoraria; Amgen: Honoraria, Speakers Bureau; Novartis: Honoraria; Astellas: Honoraria. Russell:Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees; Jazz: Research Funding, Speakers Bureau. Wei:MacroGenics: Consultancy, Honoraria; Pfizer: Honoraria; Servier: Consultancy, Honoraria, Research Funding; Walter and Eliza Hall Institute: Other: former employee and receives a fraction of its royalty stream related to venetoclax; Celgene: Consultancy, Honoraria, Research Funding; AbbVie Inc.: Consultancy, Honoraria, Research Funding; Genentech: Honoraria; Astra Zeneca: Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding.