The recommendations include a revised version of the ELN genetic categories, a proposal for a response category based on MRD status, and criteria for progressive disease.
The first edition of the European LeukemiaNet (ELN) recommendations for diagnosis and management of acute myeloid leukemia (AML) in adults, published in 2010, has found broad acceptance by physicians and investigators caring for patients with AML.
Recent advances, for example, in the discovery of the genomic landscape of the disease, in the development of assays for genetic testing and for detecting minimal residual disease (MRD), as well as in the development of novel antileukemic agents, prompted an international panel to provide updated evidence- and expert opinion-based recommendations.
Introduction
In 2010, an international expert panel, on behalf of the European LeukemiaNet (ELN), published recommendations for diagnosis and management of acute myeloid leukemia (AML).1 These recommendations have been widely adopted in general practice, within clinical trials, and by regulatory agencies. During recent years, considerable progress has been made in understanding disease pathogenesis, and in development of diagnostic assays and novel therapies.2 This article provides updated recommendations that parallel the current update to the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia.3,4 For diagnosis and management of acute promyelocytic leukemia, readers are referred to the respective recommendations.5
Methods
The panel included 22 international members with recognized clinical and research expertise in AML. The panel met 3 times. Literature searches, categorization of evidence, and arrival at consensus were done as previously.1 Relevant abstracts presented at the 2013 to 2015 meetings of the American Society of Hematology, and the 2013 to 2016 meetings of the American Association for Cancer Research, the European Hematology Association, and the American Society of Clinical Oncology were reviewed.
WHO classification
The current update of the WHO classification provides few changes to the existing disease categories (Table 1). Most importantly, a new category “myeloid neoplasms with germ line predisposition” was added (Table 2).6
Table 1.
Myeloid neoplasms with germ line predisposition, AML and related precursor neoplasms, and acute leukemias of ambiguous lineage (WHO 2016)
Table 2.
WHO classification of myeloid neoplasms with germ line predisposition and guide for molecular genetic diagnostics
AML with recurrent genetic abnormalities
The molecular basis of AML with inv(3)(q21.3q26.2) or t(3;3)(q21.3;q26.2) was revisited showing that repositioning of a GATA2 enhancer element leads to overexpression of the MECOM (EVI1) gene and to haploinsufficiency of GATA2.7,8 A new provisional entity “AML with BCR–ABL1” was introduced to recognize that patients with this abnormality should receive therapy with a tyrosine kinase inhibitor. Distinction from blast phase of chronic myeloid leukemia may be difficult; preliminary data suggest that deletion of antigen receptor genes (immunoglobulin heavy chain and T-cell receptor), IKZF1, and/or CDKN2A may support a diagnosis of AML rather than chronic myeloid leukemia blast phase.
AML with mutated NPM1 and AML with biallelic mutations of CEBPA have become full entities; the latter category was restricted to cases with biallelic mutations because recent studies have shown that only those cases define the entity and portend a favorable outcome.10-16 Both entities now subsume cases with multilineage dysplasia because presence of dysplasia lacks prognostic significance.17-19 Finally, a new provisional entity “AML with mutated RUNX1” (excluding cases with myelodysplasia-related changes) was added; it has been associated with distinct clinicopathologic features and inferior outcome.20-24
AML with myelodysplasia-related changes
Presence of multilineage dysplasia, preexisting myeloid disorder, and/or myelodysplasia-related cytogenetic changes remain diagnostic criteria for this disease category. Deletion 9q was removed from the list of myelodysplasia-related cytogenetic changes because, in addition to its association with t(8;21), it also frequently occurs in AML with NPM1 and biallelic CEBPA mutations.16,25
AML, not otherwise specified
The former subgroup acute erythroid leukemia, erythroid/myeloid type (≥50% bone marrow erythroid precursors and ≥20% myeloblasts among nonerythroid cells) was removed; myeloblasts are now always counted as percentage of total marrow cells. The remaining subcategory AML, not otherwise specified (NOS), pure erythroid leukemia requires >80% immature erythroid precursors with ≥30% proerythroblasts. French-American-British (FAB) subclassification does not seem to provide prognostic information for “AML, NOS” cases if data on NPM1 and CEBPA mutations are available.26
Myeloid neoplasms with germ line predisposition (synonyms: familial myeloid neoplasms; familial myelodysplastic syndromes/acute leukemias)
Inclusion of this new category reflects the increasing recognition that some cases of myeloid neoplasms, including myelodysplastic syndrome (MDS) and AML, arise in association with inherited or de novo germ line mutations (Table 2).6,27-30 Recognition of familial cases requires that physicians take a thorough patient and family history, including information on malignancies and previous bleeding episodes. Awareness of these cases is of clinical relevance because patients may need special clinical care.27 Affected patients, including their families, should be offered genetic counseling with a counselor familiar with these disorders.
Molecular landscape
The advent of high-throughput sequencing techniques has allowed new insights into the molecular basis of myeloid neoplasms.31-37 Similar to most sporadic human malignancies, AML is a complex, dynamic disease, characterized by multiple somatically acquired driver mutations, coexisting competing clones, and disease evolution over time.
The Cancer Genome Atlas AML substudy profiled 200 clinically annotated cases of de novo AML by whole-genome (n = 50) or whole-exome (n = 150) sequencing, along with RNA and microRNA sequencing and DNA-methylation analysis.31 Twenty-three genes were found to be commonly mutated, and another 237 were mutated in 2 or more cases, in nonrandom patterns of co-occurrence and mutual exclusivity. Mutated genes were classified into 1 of 9 functional categories: transcription factor fusions, the NPM1 gene, tumor suppressor genes, DNA methylation-related genes, signaling genes, chromatin-modifying genes, myeloid transcription factor genes, cohesin complex genes, and spliceosome complex genes.
The use of genetic data to inform disease classification and clinical practice is an active field of research. Recently, 1540 patients, intensively treated in prospective trials, were analyzed using targeted resequencing of 111 myeloid cancer genes, along with cytogenetic profiles.37 Patterns of comutations segregated AML cases into 11 nonoverlapping classes, each with a distinct clinical phenotype and outcome. Beyond known disease classes, 3 additional, heterogeneous classes emerged: AML with mutations in chromatin and RNA-splicing regulators; AML with TP53 mutations and/or chromosomal aneuploidies; and, provisionally, AML with IDH2R172 mutations.
Mutant allele fractions can be used to infer the phylogenetic tree leading to development of overt leukemia. Clonal evolution studies in patients and patient-derived xenograft models indicate that mutations in genes involved in regulation of DNA modification and of chromatin state, most commonly DNMT3A, TET2, and ASXL1, are often present in preleukemic stem or progenitor cells and occur early in leukemogenesis.38-41 Such mutations are present in ancestral cells capable of multilineage engraftment, may persist after therapy, lead to clonal expansion during remission, and cause recurrent disease.
Recent studies in large, population-based cohorts have identified recurrent mutations in epigenetic regulators (DNMT3A, ASXL1, TET2), and less frequently in splicing factor genes (SF3B1, SRSF2), to be associated with clonal hematopoietic expansion in elderly seemingly healthy subjects.42-46 The term “clonal hematopoiesis of indeterminate potential”47 has been proposed to describe this phenomenon which seems associated with increased risks of hematologic neoplasms. Preliminary data indicate that the rate of progression of clonal hematopoiesis of indeterminate potential to hematologic disease may be similar to the rate of progression of other premalignant states, such as monoclonal gammopathy of undetermined significance to multiple myeloma.
Diagnostic procedures
Morphology
At least 200 leukocytes on blood smears and 500 nucleated cells on spiculated marrow smears should be counted. A marrow or blood blast count of ≥20% is required, except for AML with t(15;17), t(8;21), inv(16), or t(16;16). Myeloblasts, monoblasts, and megakaryoblasts are included in the blast count. In AML with monocytic or myelomonocytic differentiation, monoblasts and promonocytes, but not abnormal monocytes, are counted as blast equivalents.
Immunophenotyping
Table 3 provides a list of markers helpful for establishing the diagnosis of AML,48 as well as specific lineage markers useful for defining mixed-phenotype acute leukemia.3,4
Table 3.
Expression of cell-surface and cytoplasmic markers for the diagnosis of AML and MPAL
Cytogenetics and molecular cytogenetics
Conventional cytogenetic analysis remains mandatory in the evaluation of suspected AML. Eight balanced translocations and inversions, and their variants, are included in the WHO category “AML with recurrent genetic abnormalities”.3,4 Nine balanced rearrangements and multiple unbalanced abnormalities are sufficient to establish the WHO diagnosis of “AML with myelodysplasia-related changes” when ≥20% blood or marrow blasts are present (Table 1).
Other rare balanced rearrangements are recognized.49,50 Although considered disease-initiating events, they do not formally define disease categories. They involve genes, for example, encoding epigenetic regulators (eg, KMT2A MLL, CREBBP, NSD1) or components of the nuclear pore complex (NUP98, NUP214) (Figure 1). Some rearrangements are cytogenetically cryptic, such as t(5;11)(q35.2;p15.4); NUP98-NSD1, which occurs in ∼1% of AML in younger adults and predicts a poor prognosis.51-53 Recent studies have highlighted the potential of novel sequencing technologies to discover additional AML-associated fusion genes.54-56
