Measurable residual disease (MRD) is an important biomarker in acute myeloid leukemia (AML) that is used for prognostic, predictive, monitoring, and efficacy-response assessments. The European LeukemiaNet (ELN) MRD working party evaluates standardization and harmonization of MRD in an ongoing manner and has updated the 2018 ELN MRD recommendations based on significant developments in the field. New and revised recommendations were established during in-person and online meetings, and a two-stage Delphi poll was conducted to optimize consensus. All recommendations are graded by levels of evidence and agreement. Major changes include technical specifications for next generation sequencing (NGS)-based MRD testing and integrative assessments of MRD irrespective of technology. Other topics include use of MRD as a prognostic and surrogate endpoint for drug testing; selection of the technique, material, and appropriate time points for MRD assessment; and clinical implications of MRD assessment. In addition to technical recommendations for flow- and molecular- MRD analysis, we provide MRD thresholds and define MRD response, and detail how MRD results should be reported and combined if several techniques are used. MRD assessment in AML is complex and clinically relevant, and standardized approaches to application, interpretation, technical conduct, and reporting are of critical importance.

In the international randomized phase III RATIFY trial, the multi-kinase inhibitor midostaurin significantly improved overall and event-free survival in patients 18-59 years of age with FLT3-mutated acute myeloid leukemia (AML). However, only 59% of patients on the midostaurin arm achieved protocol-specified complete remission (CR) and almost half of patients achieving CR relapsed. To explore underlying mechanisms of resistance, we studied patterns of clonal evolution in patients with FLT3-internal tandem duplications (ITD) positive AML who were entered on the RATIFY or the AMLSG 16-10 trial and received treatment with midostaurin. To this end, paired samples from 54 patients obtained at time of diagnosis and at time of either relapsed or refractory disease were analyzed using conventional Genescan-based testing for FLT3-ITD as well as whole exome sequencing. At the time of disease resistance or progression, almost half of the patients (46%) became FLT3-ITD negative, but acquired mutations in signaling pathways (e.g. MAPK), thereby providing a new proliferative advantage. In cases with FLT3-ITD persistence, the selection of resistant ITD-clones was found in 11% as potential drivers of disease. In 32% of cases, no FLT3-ITD mutational change was observed suggesting either resistance mechanisms bypassing FLT3-inhibition or loss of midostaurin inhibitory activity due to inadequate drug levels. In summary, our study provides novel insights into the clonal evolution and resistance mechanisms of FLT3-ITD mutated AML under treatment with midostaurin in combination with intensive chemotherapy.

ABSTRACTand clinical impact of these mutations in the context of other clinical and genetic factors in a well-defined population of patients intensively treated in trials of the GermanAustrian AML Study Group (AMLSG). Methods PatientsA total of 1696 younger AML patients (18 to 61 years) were studied. Patients were enrolled in prospective treatment protocols of the AMLSG), namely AML HD98A 12 (n=733; NCT00146120), AMLSG 07-04 13 (n=893; NCT00151242), and APL HD95 14 (n=70) for the patients with acute promyelocytic leukemia (APL). The clinical studies were approved by the local ethics review committees and all patients gave informed consent for both treatment and cryopreservation of leukemia samples according to the Declaration of Helsinki. The only criterion to include patients in our study was the availability of a pretreatment bone marrow or peripheral blood specimen for analysis of ASXL1 mutations. Cytogenetic and additional molecular analyses were performed as previously described. 15-19 ASXL1 mutation analysisA detailed description of the ASXL1 mutation analysis is provided in the Online Supplementary Material. Briefly, genomic DNA was used as a template for polymerase chain reactions to amplify several fluorescently-labeled DNA fragments covering the entire exon 12 (AMLSG 07-04) or regions within exon 12 (AML HD98A and APL HD95) identified as main mutation clusters in AML. 6,20 Amplicons were screened for mutations by a GeneScan-based fragment analysis (Online Supplementary Figures S1 and S2). Samples classified as mutated after the GeneScan analysis (Online Supplementary Figure S2) were further analyzed by direct sequencing to validate the mutation and to determine the mutation type. Statistical analysisStatistical analyses of clinical outcome were performed according to previous reports. 16 The median follow-up for survival was calculated according to the method of Korn. 21 The definition of complete remission (CR), event-free survival (EFS), relapse-free survival (RFS), and overall survival (OS) as well as cytogenetic categorization into favorable-, intermediate-, and adverse-risk groups followed recommended criteria. 22 Pairwise comparisons between patients' characteristics (covariates) were performed using the Mann-Whitney test for continuous variables and the Fisher exact test for categorical variables. The Kaplan-Meier method was used to estimate the distribution of EFS, RFS and OS. 23 Estimation of confidence intervals for the survival curves was based on the Greenwood formula for standard error estimation. A logistic regression model was used to analyze associations between baseline characteristics and the achievement of CR. A Cox model was used to identify prognostic variables. 24 In addition to ASXL1 mutation status, age, sex, hemoglobin level, logarithm of white blood cell count, type of AML (de novo, secondary AML, therapy-related AML), percentage of peripheral blood and bone marrow blasts, cytogenetic risk group, 22 and mutational status of NPM1, FLT3 (ITD and TKD),), RUNX1, MLL (PTD), and DN...

In acute lymphoblastic leukemia (ALL), central nervous system (CNS) involvement is a major clinical concern. Despite nondetectable CNS leukemia in many cases, prophylactic CNS-directed conventional intrathecal chemotherapy is required for relapse-free survival, indicating subclinical CNS manifestation in most patients. However, CNS-directed therapy is associated with long-term sequelae, including neurocognitive deficits and secondary neoplasms. Therefore, molecular mechanisms and pathways mediating leukemia-cell entry into the CNS need to be understood to identify targets for prophylactic and therapeutic interventions and develop alternative CNS-directed treatment strategies. In this study, we analyzed leukemia-cell entry into the CNS using a primograft ALL mouse model. We found that primary ALL cells transplanted onto nonobese diabetic/severe combined immunodeficiency mice faithfully recapitulated clinical and pathological features of meningeal infiltration seen in patients with ALL. ALL cells that had entered the CNS and were infiltrating the meninges were characterized by high expression of vascular endothelial growth factor A (). Although cellular viability, growth, proliferation, and survival of ALL cells were found to be independent of VEGF, transendothelial migration through CNS microvascular endothelial cells was regulated by VEGF. The importance of VEGF produced by ALL cells in mediating leukemia-cell entry into the CNS and leptomeningeal infiltration was further demonstrated by specific reduction of CNS leukemia on in vivo VEGF capture by the anti-VEGF antibody bevacizumab. Thus, we identified a mechanism of ALL-cell entry into the CNS, which by targeting VEGF signaling may serve as a novel strategy to control CNS leukemia in patients, replacing conventional CNS-toxic treatment.

Monitoring of measurable residual disease (MRD) provides prognostic information in patients with Nucleophosmin1 mutated (NPM1mut) acute myeloid leukemia (AML) and represents a powerful tool to evaluate treatment effects within clinical trials. We determined NPM1mut transcript levels (TL) by RQ-PCR and evaluated the prognostic impact of NPM1mut MRD and the effect of gemtuzumab ozogamicin (GO) on NPM1mut TL and the cumulative incidence of relapse (CIR) in patients with NPM1mut AML enrolled in the randomized phase III AMLSG 09-09 trial. 3733 bone marrow (BM) and 3793 peripheral blood (PB) samples from 469 patients were analyzed. NPM1mut TL log10 reduction ≥3 and achievement of MRD negativity in BM and PB were significantly associated with a lower CIR rate, after two treatment cycles and at end of treatment (EOT). In multivariate analyses, MRD positivity consistently revealed as poor prognostic factor in BM and PB. With regard to treatment effect, the median NPM1mut TL were significantly lower in the GO-Arm across all treatment cycles, resulting in a significantly higher proportion of patients achieving MRD negativity at EOT (56% vs 41%; P=.01). The betterreduction of NPM1mut TL after two treatment cycles in MRD-positive patients by the addition of GO led to a significantly lower CIR rate (4-year CIR 29.3% vs 45.7%, P=.009). In conclusion, the addition of GO to intensive chemotherapy in NPM1mut AML resulted in a significantly better reduction of NPM1mut TL across all treatment cycles leading to a significantly lower relapse rate. The AMLSG 09-09 trial was registered at www.clinicaltrials.gov as #NCT00893399.