2021 Update on MRD in acute myeloid leukemia: a consensus document from the European LeukemiaNet MRD Working Party.

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 evaluated 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 2-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-based MRD testing and integrative assessments of MRD irrespective of technology. Other topics include use of MRD as a prognostic and surrogate end point 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.

Protein phosphatase 4 regulatory subunit 2 (PPP4R2) is recurrently deleted in acute myeloid leukemia and required for efficient DNA double strand break repair.

We have previously identified a recurrent deletion at chromosomal band 3p14.1-p13 in patients with acute myeloid leukemia (AML). Among eight protein-coding genes, this microdeletion affects the protein phosphatase 4 regulatory subunit 2 (PPP4R2), which plays an important role in DNA damage response (DDR). Investigation of mRNA expression during murine myelopoiesis determined that Ppp4r2 is higher expressed in more primitive hematopoietic cells. PPP4R2 expression in primary AML samples compared to healthy bone marrow was significantly lower, particularly in patients with 3p microdeletion or complex karyotype. To identify a functional role of PPP4R2 in hematopoiesis and leukemia, we genetically inactivated Ppp4r2 by RNAi in murine hematopoietic stem and progenitor cells and murine myeloid leukemia. Furthermore, we ectopically expressed PPP4R2 in a deficient human myeloid leukemic cell line. While PPP4R2 is involved in DDR of both hematopoietic and leukemic cells, our findings indicate that PPP4R2 deficiency impairs de-phosphorylation of phosphorylated key DDR proteins KRAB-domain associated protein 1 (pKAP1), histone variant H2AX (γH2AX), tumor protein P53 (pP53), and replication protein A2 (pRPA2). Potential impact of affected DNA repair processes in primary AML cases with regard to differential PPP4R2 expression or 3p microdeletion is also supported by our results obtained by gene expression profiling and whole exome sequencing. Impaired DDR and increased DNA damage by PPP4R2 suppression is one possible mechanism by which the 3p microdeletion may contribute to the pathogenesis of AML. Further studies are warranted to determine the potential benefit of inefficient DNA repair upon PPP4R2 deletion to the development of therapeutic agents.

ASXL1 mutations in younger adult patients with acute myeloid leukemia: a study by the German-Austrian Acute Myeloid Leukemia Study Group.

We studied 1696 patients (18 to 61 years) with acute myeloid leukemia for ASXL1 mutations and identified these mutations in 103 (6.1%) patients. ASXL1 mutations were associated with older age (P<0.0001), male sex (P=0.041), secondary acute myeloid leukemia (P<0.0001), and lower values for bone marrow (P<0.0001) and circulating (P<0.0001) blasts. ASXL1 mutations occurred in all cytogenetic risk-groups; normal karyotype (40%), other intermediate-risk cytogenetics (26%), high-risk (24%) and low-risk (10%) cytogenetics. ASXL1 mutations were associated with RUNX1 (P<0.0001) and IDH2(R140) mutations (P=0.007), whereas there was an inverse correlation with NPM1 (P<0.0001), FLT3-ITD (P=0.0002), and DNMT3A (P=0.02) mutations. Patients with ASXL1 mutations had a lower complete remission rate (56% versus 74%; P=0.0002), and both inferior event-free survival (at 5 years: 15.9% versus 29.0%; P=0.02) and overall survival (at 5 years: 30.3% versus 45.7%; P=0.0004) compared to patients with wildtype ASXL1. In multivariable analyses, ASXL1 and RUNX1 mutation as a single variable did not have a significant impact on prognosis. However, we observed a significant interaction (P=0.04) for these mutations, in that patients with the genotype ASXL1(mutated)/RUNX1(mutated) had a higher risk of death (hazard ratio 1.8) compared to patients without this genotype. ASXL1 mutation, particularly in the context of a coexisting RUNX1 mutation, constitutes a strong adverse prognostic factor in acute myeloid leukemia.