Table of contents :

acute myeloid leukemias (AML)  FAB classification M0 / undifferentiated M1 M2 M3 / acute promyelocytic leukemia (APL)  therapy M4 / myelomonocytic M5 / monocytic M6 / erythroleukemia M7 / megakaryocytic mixed lineage leukemias WHO classification : acute myeloid leukemia with recurrent genetic abnormalities acute myeloid leukemia with multilineage dysplasia acute myeloid leukemia and myelodysplastic syndromes, therapy related acute myeloid leukemia, not otherwise categorized (AML-NOC) laboratory examinations therapy prognosis

chronic myeloproliferative disorders (CMPDs) chronic myeloid leukemia  laboratory examinations therapy prognosis polycythemia vera  essential thrombocytemia  chronic idiopathic myelofibrosis  chronic eosinophilic leukemia (CEL) (and the hypereosinophilic syndrome (HES)) chronic neutrophilic leukemia

Pathogenesis :

• mutations in tyrosine kinases => proliferation defects => acute or chronic leukemia => acute leukemia
• down-regulation of HAT and upregulation of HDAC => differentiation defects => acute leukemia

normocytic and normochromic anemia, leukocytosis with relative neutropenia, thrombocytosis with thrombocytopathy

Clinical course :

• acute myeloproliferative disorders (AMPDs)
• acute myeloid (or myelogenous) leukemias (AML) / acute granulocytic leukemia / acute non-lymphoid leukemias (ANLL) represents a group of clonal hematopoietic stem cell disorders in which both failure to differentiate and overproliferation in the stem cell compartment result in accumulation of non-functional cells termed myeloblasts (> 20% in bone marrow). At least 20% of the blasts must have surface antigens associated with myeloid differentiation, most commonly CD33 or CD13. According to Rabbits master genes theory AML is an accumulation rather than a proliferation disease. Only 1 in 1 million leukemic blasts appears to be a true stem cell, according to the capacity to propagate and sustain human leukemia in immunologically susceptible mice^ref
• type I blast : no granules, fine chromatine, high nucleus/cytoplasm ratio and commonly evident nucleoli
• type II blast : rare azurophilic granules and smaller nucleus/cytoplasm ratio
• promyelocytes : eccentric nucleus, Golgi apparatus, addensed chromatin with conserved nucleolus, many granules and low nucleus/cytoplasm ratio
• myeloblastoma : a focal malignant tumor, observed in AML, composed of myeloblasts or early myeloid precursors occurring outside of the bone marrow
• chloroma / chloroleukemia / chloromatous or granulocytic sarcoma : a malignant green-colored tumor arising from myeloid tissue, associated with myelogenous leukemia and occurring anywhere in the body. Besides containing green pigment, which has no clear metabolic role and is principally myeloperoxidase, chloroma tissue demonstrates a bright red fluorescence under ultraviolet light
Epidemiology : most types affect primarily middle-aged to elderly people; incidence ranges from < 1 per 100,000/year in babies to 2.5-3.5 per 100,000/year in children aged 15 years to 17.9 per 100,000/year in people aged > 65 years; more common in males than females. The median at age at presentation is about 70 years, and 3 men are affected for every 2 women.
Aetiology :
• de novo AML : usually unknown
• environmental factors :
• radiation : People who have survived atomic bombs are at high risk of AML, and Nakanishi and colleagues^ref2 found that abnormalities of chromosomes 5 and 7 are much more common in such patients than in patients born before 1945 without bomb exposure. Leukaemia is also common in workers in the nuclear industry^ref,3 but not in people living near nuclear power plants.4 Extensive flying in commercial jet planes is a less appreciated source of radiation exposure; Gundestrup and Storm reported a 5.1-times (95% CI 1.03–14.91) increased incidence of AML in Danish male cockpit crew who had flown for > 5000 h^ref.5
• AML associated with benzene exposure (and cytotoxic chemotherapy; see below)^ref6 are characterised by aberrations of chromosome 5 or 7 or both. Cigarette smoking is the most common source of benzene exposure. Smoking confers an average 1.2–2.3 times increase in the incidence of AML, with the greatest risk in current smokers^ref.7 Cigarette-induced AML seems only variably associated^ref8 with abnormalities in chromosomes 5 and 7 and is also accompanied by trisomy^ref9 of chromosome 8 and, particularly, by a balanced translocation between chromosomes 8 and 21^ref10 or its morphological signature, French–American–British (FAB) subtype M2^ref.11
• apart from the use of cigarettes and alcohol, very few mothers of AML children reported exposure to known topo-II inhibitors. Significant case-control differences were apparent for ingestion of several groups of drugs, including herbal medicines and drugs classified as "DNA-damaging," and for exposure to pesticides with the last 2 being largely attributable, respectively, to one nonsteroidal anti-inflammatory drug, dipyrone, and mosquitocidals (including Baygon). Elevated odds ratios were observed for MLL⁺ (but not MLL^-) leukemias (2.31 for DNA-damaging drugs, P = 0.03; 5.84 for dipyrone, P = 0.001; and 9.68 for mosquitocidals, P = 0.003). Although it is unclear at present whether these particular exposures operate via an effect on topo-II, the data suggest that specific chemical exposures of the fetus during pregnancy may cause MLL gene fusions. Given the widespread use of dipyrone, Baygon, and other carbamate-based insecticides in certain settings, confirmation of these apparent associations is urgently required^ref. Environmental tobacco smoke (ETS) is not associated with adult AML^ref.
• the MLL 11q23 translocation arises in utero and is present in 75% of infant leukemias. That MLL⁺ AML can arise following chemotherapy with DNA topoisomerase II (DNAt2) inhibitors suggests that these substances, which also occur naturally in foods, may contribute toward infant leukemia. Maternal consumption of dietary DNAt2 inhibitors during pregnancy could increase the risk of infant leukemia, particularly AML(MLL⁺). This Children's Oncology Group case-control study consisted of 240 incident cases of infant acute leukemia [AML and acute lymphoblastic leukemia (ALL)] diagnosed during 1996 to 2002 and 255 random digit dialed controls. Maternal diet during pregnancy was determined through a food frequency questionnaire. An index of specific foods identified a priori to contain DNAt2 inhibitors as well as vegetables and fruits were created and analyzed using unconditional logistic regression. There was little evidence of an association between the specific DNAt2 index and leukemia overall and by subtype. An exception was AML(MLL⁺); odds ratios (95% confidence intervals) comparing the second to fourth quartiles to the first were 1.9 (0.5-7.0), 2.1 (0.6-7.7), and 3.2 (0.9-11.9), respectively (P for trend = 0.10). For the vegetable and fruit index, there were significant or near-significant inverse linear trends for all leukemias combined, ALL(MLL⁺), and AML(MLL^-). Overall, maternal consumption of fresh vegetables and fruits during pregnancy was associated with a decreased risk of infant leukemia, particularly MLL⁺. However, for AML(MLL⁺) cases, maternal consumption of specific DNAt2 inhibitors seemed to increase risk. Although based on small numbers, these data provide some support for distinct etiologic pathways in infant leukemia^ref.
The -5/-7 abnormalities associated with radiation, occupational benzene exposure, and alkylating agents are identical to those typical of spontaneously arising AML. The incidence of de-novo AML associated with -5/-7 rises with age, whereas that of AML associated with balanced translocations does not^ref.13
• inherited conditions
• familial AML
• identical or nonidentical sibling with AML
• clastogenias
• Wiskott-Aldrich syndrome
• dyskeratosis congenita
• combined immunodeficiency syndrome
• congenital agranulocytosis
• neurofibromatosis type I
• Shwachman-Diamond syndrome (SDS)
• chromosome 21q disorder, including Down syndrome
• carriers of the glutamine-encoding allele at codon 751 of the xeroderma pigmentosum group D (XPD) DNA repair gene were significantly more likely to have a karyotype associated with a less favourable prognosis, and hypothesized that this observation was driven by an association between the codon 751 variant and risk of developing AML with specific structural abnormalities. Using a case series of 927 AML patients we show here that the XPD codon 751 glutamine-encoding variant significantly associates with risk of developing AML with a chromosome 5q deletion (odds ratio (OR) 2.09, 95% confidence interval (CI) 1.14-3.81, n=69, p=0.02) or a chromosome 7q deletion (OR 2.27, 95% CI 1.09-4.71, n=47, p=0.03), but not with any other commonly recurring cytogenetic lesion^ref
• secondary AML
• therapy-related AML (t-AML) (chemotherapy (and radiotherapy to a lesser extent)^ref for a solid cancer or lymphoproliferative syndromes) (13%)^ref
• t-APL (3%)
There are 2 main types of therapy-related AML^ref :

	chromosome abnormality	latency	long term survival	chemotherapy drugs
alkylating agents (classic tMDS-tAML)ref	del(5q), -5, del(7q), -7	3–10 years (5-7)	poor	chlorambucil, BCNU, CCNU, Cytoxan
DNA topoisomerase II inhibitors	They usually have no preleukemic phase, and showed normal karyotype or cytogenetic rearrangements specific to de novo AMLref. 11q23 and 21q22 rearrangements predominated, whereas t(8;21), inv(16), and t(15;17) (which is characteristic of acute promyelocytic leukaemiaref) were less often seen, and other rearrangements were rarely observedref1, ref2.	6 months-5 years	poor	epipodophyllotoxins such as etoposide or teniposide, and anthracycline (doxorubicin) or anthracenedione (mitoxantrone)
various agents	t(15;17), inv(16)	2-3 years	good	bimolane

tMDS and tAML have also been reported after autologous HSCT^ref. In addition, prolonged use of hydroxyurea in chronic myeloproliferative disorders might increase the patients’ risk of progression to AML^ref
• chronic myeloproliferative disorders
• myelodysplastic syndromes
• bi- or tricytopenia with hyperplastic marrow
• paroxysmal nocturnal hemoglobinuria
• aplastic anemia
• eosinophilic fasciitis
• multiple myeloma
Pathogenesis : the number of people exposed to environmental causes of AML probably far exceeds the number who develop the disease. Development of AML after exposure may reflect genetic variation in enzymes that detoxify benzene and other carcinogens, such as NAD(P)H quinone oxidoreductase 1 (NQO1)^ref.14 A single 609C-T substitution in NQO1, lowers NQO1 actvity; if 2 alleles are mutant, enzyme activity is absent. About 20% of northern Europeans and white Americans are heterozygous for the 609T NQO1 variant, and 20% of Asian people are homozygous. Larson and co-workers^ref15 studied a population among which 34% would have been expected to be 609T heterozygotes and 5% 609T homozygotes. However, 23 (41%) of their 56 patients with therapy-related AML were heterozygotes and 11% homozygotes (p=0.04). Among 45 patients with either therapy-related or de novo AML and -5/-7, 38% were heterozygous and 16% homozygous (p=0.002 compared with the expected frequencies). NQO1 polymorphisms were not associated with balanced chromosomal translocations in patients with AML. Reduced NQO1 activity was 10.47-times more common (95% CI 1.13–1.90) among 498 British patients with de-novo AML than among 838 controls matched for age, sex, race, and local physician^ref;16 NQO1 polymorphisms were over-represented in patients with inv(16), a pericentric inversion of chromosome 16. Members of the cytochrome P450 family are also involved in detoxification. Allelic variants of CYP1A1 are no more common in AML than in the general population, but the CYP1A1*2B (Val) allele is 15.9-times more common (95% CI 3·7–68·5) in patients with -5/-7 and RAS mutations than in other patients with AML^ref.17 Gilliland and colleagues suggested that AML blasts develop from normal blasts affected by 2 types of genetic damage^{ref1, ref2}18 and 19 : an activating mutation in a signal transduction pathway and a mutation in a transcription factor are required for leukemogenesis
• The first (class 1) results in constitutive activation of cell-surface receptors, such as RAS, or receptor tyrosine kinases, such as FLT3 and c-KIT. Through various downstream pathways, constitutive activation confers a survival or proliferative advantage leading to clonal expansion of the affected HSCs. In mouse models, abnormalities in RAS, FLT3, or c-KIT by themselves produce only a myeloproliferative disorder and not frank AML
• The second type of lesion (class 2) exemplified by overexpression of HOX genes or formation of fusion genes, resulting from the t(8;21) or inv(16) abnormalities block myeloid differentiation but, like class 1 lesions, do not cause leukaemia in mouse models^ref.20
AML might develop only when both classes of lesion are present. Support for this 2-hit model comes from demonstration that class 1 and class 2 lesions occur together more commonly than do 2 class 1 or 2 class 2 lesions^{ref1, ref2, ref3, ref4, ref5, ref6, ref7, ref8}.18, 19, 20, 21, 22, 23, 24 and 25 The two-hit model is attractive in explaining the origin of t(8;21) and inv(16) AML, each of which is often accompanied by c-KIT mutations^{ref1, ref2, ref3, ref4},21, 22, 23, 24 and 25 and AML characterised by FLT3 aberrations^{ref1, ref2}26 and 27 or RAS mutations^ref.28 Indeed, several drugs used to treat AML target FLT3 aberrations and the RAS signalling pathway^ref.29 This model, however, provides a less cogent explanation for -5/-7 AML but could be modified to account for the role of epigenetic factors^ref.30 Specifically, various putative tumour suppressor genes are hypermethylated and thus silenced in AML^ref.31 Because hypermethylation, once present, is permanent, it is functionally equivalent to a genetic mutation. Evidence for epigenetic changes in AML pathogenesis comes from the clinical activity of hypomethylating agents, such as decitabine^ref,32 and of histone deacetylase inhibitors, such as valproic acid, which might allow transcription of genes silenced in AML^ref.33 Various AML treatments eliminate circulating blasts more effectively than those in marrow, probably because marrow blasts are protected from the apoptosis induced by chemotherapy by the marrow stroma^ref.34 This protective effect seems to be mediated through an interaction between the chemokine receptor CXCR4, expressed on blasts, and its stromal ligand SDF-1; the interaction may also govern release of blasts from marrow to the circulation^ref.35
• AML with defined karyotype (45-50%) :
• nucleophosmin (NPM1) exon-12 gene mutations^ref (27.5%^ref-35%; 45.7%^ref-62% of normal karyotype AMLs) : founding mutation, 19 different out-of-frame mutations. The NPM1 gene encodes for a multifunctional nucleo-cytoplasmic shuttling protein which is mainly localized in the nucleolus. NPM1 mutations occur in 50-60% of adult AML with normal karyotype and generate NPM mutants that localize aberrantly in the leukemic cells cytoplasm; hence the term NPM-cytoplasmic positive (NPMc⁺ AML). Cytoplasmic NPM accumulation is caused by the concerted action of 2 alterations at mutant C-terminus, i.e. changes of tryptophan(s) 288 and 290 (or only 290) and creation of an additional nuclear export signal (NES) motif. NPMc⁺ AML shows increased frequency in adults and female sex, high WBC counts, wide morphologic spectrum, multilineage involvement, high frequency of FLT3-ITD (66$), CD34-negativity, and distinct gene expression profile. Analysis of mutated NPM has important clinical and pathological applications. Immunohistochemical detection of cytoplasmic NPM predicts NPM1 mutations and helps rationalize cytogenetic/molecular studies in AML. NPM1 mutations in absence of FLT3-ITD identify a prognostically favourable subgroup in the heterogeneous AML-NK category. Due to their frequency and stability, NPM1 mutations may become a new tool for monitoring minimal residual disease in AML-NK. Future studies should focus on clarifying how NPM mutants promote leukemia, integrating NPMc⁺ AML in the upcoming World Health Organization leukemia classification, and eventually developing specific anti-leukemic drugs^ref. Normal nucleophosmin is a chaperon of preribosomal particles from nucleus to cytoplasm, has a role in centrosome duplication, enhances acetylation-dependent chromatin transcription^ref and inactivates p53 and p19ARF in the cytoplasm. NPM1 mutations associate inversely with the occurrence of CEBPA- and N-RAS mutations. With respect to gene expression profiling, AML cases with an NPM1 mutation cluster in specific subtypes of AML with previously established gene expression signatures, are highly associated with a homeobox gene-specific expression signature and can be predicted with high accuracy. Patients with intermediate cytogenetic risk AML without FLT3 ITD mutations but with NPM1 mutations have a significantly better OS and EFS than those without NPM1 mutations^ref. Finally, in multivariable analysis NPM1 mutations express independent favorable prognostic value with regard to overall-, event free- and disease free survival^ref
• activating FLT3 mutations (24-27% of de novo AMLs^ref, 42% of acute promyelocytic leukemia (APL), 17% of secondary AML^ref, and 4% of t-AML) :
• internal tandem duplication (ITD) in the juxtamembrane (JM) domain-coding sequence (FLT3-length mutations (FLT3-LM) / FLT3-ITD) can usually be detected by gel electrophoresis of the PCR products generated from amplifying exons 14 and 15 of the FLT3 gene, in which most ITDs occur. The PCR primers will generate a wild-type band and a larger FLT3 ITD band, which can be preparated by gel electrophoresis. ITD is  found in
• 20-25% of adult AML, more common in cases with MLL intragenic abnormalities (33%) than those with MLL translocation (8%)
• at a lower frequency in childhood AML
FLT3-ITD is associated with leukocytosis and a poor prognosis, especially in patients with normal karyotype.
• point mutations in the protein tyrosine kinase domain (TKD) (FLT3-TKD)
• D835 : mutation (D835Y >> D835V, D835H, D835E, and D835N)/deletion are found in 6% of adult AML; they are present in > 20% of cases with MLL intragenic abnormalities compared with 10% of AML with MLL translocation and 5% of adult AML with normal MLL status^ref.
• Y842H
The detection of FLT3 point mutations is more complicted, but can also be achieved by PCR. The double-strand PCR product is denaturated, then run on a single-strand conformational polymorphism (SSCP) gel, which allows the single strands to re-anneal, forming a unique secondary structure. A base-pair mutation results in a different secondary structure, which migrates differently on the gel than the structure of the wild-type sequence. The abnormal bands can then be excised from the gel and sequenced for confirmation.
Anyway FLT3 mutations are not primary mutations. There is some evidence that the ratio of mutant to wild-types alleles might determine the pathogenesis of FLT3 mutations. This can be assessed by fluorescent-labelled PCR, whereby the labelled PCR products are separatede according to size by migration through a capillary system, with the intensity of the products (relating to relative abundance) determined by laser excitation. Normally FLT3 has an activating phosphorylation at Y416 and a deactivating phosphorylation at Y527.
• translocations => chimeric fusion proteins => more immunogenic => good prognosis
• t(8;21)(q22;q22) (8-12%) fuses the AML1 / RUNX1 / core-binding factor 2 (CBF2) DNA-binding transcription factor to the ETO corepressor that associates with HDAC complexes. AML1 is homologous to the runt gene of Drosophila : it binds as a heterodimer, partnered with CBFß, and upregulates CD13, GM-CSF, MPO, IL-3, and the TcR.  Instead ETO encodes the human homologue of the Drosophila Nervy protein. Analyses have demonstrated that AML1-ETO blocks AML1 function and requires additional mutagenic events to promote leukemia. The loss of the molecular events of AML1-ETO C-terminal NCoR/SMRT-interacting domain transforms AML1-ETO into a potent leukemogenic protein. Contrary to full-length AML1-ETO, the truncated form promotes in vitro growth and does not obstruct the cell-cycle machinery. These observations suggest a previously uncharacterized mechanism of tumorigenesis, in which secondary mutation(s) in molecular events disrupting the function of a domain of the oncogene promote the development of malignancy^ref. Mutations in AML1-ETO and FLT3 length mutation (FLT3-LM) are 2 of the most common genetic alterations seen in patients with AML, but neither mutation alone can cause leukemia in animal models : AML1-ETO cooperates with FLT3-LM, causing hematopoietic progenitor cells to become malignant and potently triggering rapid and aggressive acute leukemia in mice. Moreover, in a series of 135 patients with AML1-ETO-positive AML, the most frequently identified class of additional mutations affected genes involved in signal transduction pathways including FLT3-LM or mutations of KIT and NRAS^ref. Associated with loss of Y in males or of X in females over half the cases. It has been identified in 15% of all cases of AML, including 40–50% of FAB M2 subtype and rare cases of M0, M1 and M4 subtypes. The most commonly known AML1-ETO fusion protein (full-length AML1-ETO) from this translocation has 752 amino acids and contains the N-terminal portion of RUNX1 (also known as AML1, CBF2 or PEBP2B), including its DNA binding domain, and almost the entire RUNX1T1 (also known as MTG8 or ETO) protein. Although alterations of gene expression and hematopoietic cell proliferation have been reported in the presence of AML1-ETO, its expression does not lead to the development of leukemia. The alternatively spliced isoform AML1-ETO9a, that includes an extra exon, exon 9a, of the ETO gene, encodes a C-terminally truncated AML1-ETO protein of 575 amino acids : expression of AML1-ETO9a leads to rapid development of leukemia in a mouse retroviral transduction–transplantation model. More importantly, coexpression of AML1-ETO and AML1-ETO9a results in the substantially earlier onset of AML and blocks myeloid cell differentiation at a more immature stage. These results indicate that fusion proteins from alternatively spliced isoforms of a chromosomal translocation may work together to induce cancer development^ref. High frequency of granulocytic sarcomas
• inv16 => MYH11-core-binding factor b (CBFB) (7-10%)
• t(15;17)(q22;q11-q21) fuses RARa-PML (in AML M3 / APL) (10%)
• 11q23 abnormalities (mixed lineage leukemia (MLL)-var) (10-12%) : frequently altered in ALL, primary AML, and especially in AML secondary to the use of topoisomerase II inhibitors. MLL is homologous to the trithorax gene of Drosophila and displays many features of a transcription factor and of a DNA methyl transferase. There are >50 known partner genes with which it is able to form in-frame fusions.
• fusion with chromosome 1 :
• MLL-MLLT11 / AF1Q (1q21)
• fusion with chromosome 4 :
• MLL-AFF1 / AF4 (4q21) (the most prevalent MLL fusion protein) binds to the CDKN1B promoter in vivo and depending on the background cell type, MLL-AF4 inhibits or activates CDKN1B expression^ref
• fusion with chromosome 6 : MLL-MLLT4 / AF6 (6q27)
• fusion with chromosome 9 :
• MLL-MLLT3 / AF9 (9q22) (7%). Associated with monocytic leukemia. Leukaemia stem cells (LSC) from leukaemias initiated in committed granulocyte macrophage progenitors through introduction of the MLL–AF9 fusion protein encoded by the t(9;11)(p22;q23). The LSC were capable of transferring leukaemia to secondary recipient mice when only 4 cells were transferred, and possessed an immunophenotype and global gene expression profile very similar to that of normal granulocyte macrophage progenitors. However, a subset of genes highly expressed in normal HSCs was re-activated in LSC. LSC can thus be generated from committed progenitors without widespread reprogramming of gene expression, and a leukaemia self-renewal-associated signature is activated in the process^ref.
• MLL-FNBP1 / FBP17 (9q34)
• fusion with chromosome 10 :
• MLL-ABI1 (10p11.2)
• MLL-MLLT10 / AF10 (10p12)
• fusion with chromosome 19 :
• MLL-ELL (19p13.1) (90%)
• MLL-MLLT1 / ENL (19p13.3) (10%)
• MLL-MLLT7 / AFX1 (Xq13.1)
• MLL-CBP
• MLL-GAS7 (17p31)
• MLL-SEPT5 / PNUTL1 (22q11.21)
• MLL-SEPT6 (Xq24)
• MLL-SEPT9 / MSF (17q25)
• MLL-RARa (15q22)
• [MLL-AFF1 / MLLT2 (4q21)
• MLL-EPS15 / MLLT5 (1p32)
• MLL-MLLT6 (17q21)]
Upon transplantation into immunodeficient mice, primitive human hematopoietic cells expressing a MLL fusion gene generated myeloid or lymphoid acute leukemias, with features that recapitulated human diseases. Analysis of serially transplanted mice revealed that the disease is sustained by leukemia-initiating cells (L-ICs) that have evolved over time from a primitive cell type with a germline immunoglobulin heavy chain (IgH) gene configuration to a cell type containing rearranged IgH genes. The L-ICs retained both myeloid and lymphoid lineage potential and remained responsive to microenvironmental cues. The properties of these cells provide a biological basis for several clinical hallmarks of MLL leukemias^ref.
Minor translocations :
• AML1 / RUNX1-EVI1
• ETV6-ABL
• ETV6-CDX2
• ETV6-CHIC2
• ETV6-MN1
• ETV6-EVI1
• FGFR1-FOP
• FUS-ERG
• MOZ-CBP
• NPM1-MLF1
• NUP98-HOXA9
• NUP214-DEK t(6:9) is usually seen in young patients and carries a poor prognosis. Its normal function is unknown, but DEK localizes to the nucleus.
• RARa-NUMA1
• RARa-ZNF145
• RBM15-MAL
• PDGFRB-TRIP11
• TCF3-PBX1
• TCL1A-TRA
• trisomy 8 (8% isolated, 12% with additional mutations)
• 5q, 5mono (3-4%)
• 7q-, 7mono (4-6%)
• H3 methylase hDOT1L activates Hox genes, whose increased activity is closely tied to AML^{ref1, ref2}.
• 20q del : DATF1 / death inducer-obliterator (Dido) gene gives rise to at least 3 polypeptides (Dido1, Dido2, and Dido3) through alternative splicing. Targeting of murine Dido caused a transplantable disease whose symptoms and signs suggested MDS/MPDs. Furthermore, 100% of human MDS/MPD patients analyzed showed Dido expression abnormalities, which was also found in other myeloid but not lymphoid neoplasms or in healthy donors. Dido might be one of the tumor suppressor genes at chromosome 20q and that the Dido-targeted mouse may be a suitable model for studying MDS/MPD diseases and testing new approaches to their diagnosis and treatment^ref.
• CEBPa mutated in 7-10% of AML (mainly M1-M2, not carrying the t(8;21) or the inv16 abnomalities, as they down-regulate it)^ref
• SALL4, a human homolog to Drosophila spalt, is a novel zinc finger transcriptional factor essential for development. SALL4 isoforms (SALL4A and SALL4B) are constitutively expressed in human primary AML (N=81). SALL4B transgenic mice developed MDS-like features and subsequently AML that was transplantable. Increased apoptosis associated with dysmyelopoiesis was evident in transgenic mouse marrow and CFU assays. Both isoforms could bind to b-catenin and synergistically enhanced the Wnt/b-catenin signaling pathway. The constitutive expression of SALL4 causes MDS/AML, most likely through the Wnt/b-catenin pathway^ref.
• activating mutations in RAS, predominantly NRAS, are common in myeloid malignancies. Previous studies in animal models have shown that oncogenic NRAS is unable to induce myeloid malignancies effectively and it was suggested that oncogenic NRAS might only act as a secondary mutation in leukemogenesis. The leukemogenecity of NRAS was examined using an improved mouse bone marrow transduction and transplantation model. Oncogenic NRAS rapidly and efficiently induced CMML- or AML-like disease in mice, indicating that mutated NRAS can function as an initiating oncogene in the induction of myeloid malignancies. In addition to CMML and AML, NRAS induced mastocytosis in mice^ref
• GNNK- and GNNK+ c-KIT isoforms^ref
• 15% of AML have unknown founding mutations
• complex karyotype
• unknown karyotype (40%)
In univariate and multivariate analysis high levels of PKC, ERK, pERK, and pAKT, but not AKT, were adverse factors for survival as was the combination variable PKC-ERK2&pERK2-pAKT. Survival progressively decreased as the number of activated pathways increased. Patients were more likely to have none or all 3 pathways activated than was predicted based on the frequency of individual pathway activation strongly suggesting that cross-activation occurred^ref. Interaction between the b₁ integrin VLA4 on AML cells and fibronectin on bone-marrow stromal cells increases resistance to ainokis after treatment with daunorubicin and araC and allows the development of minimal residual disease (MRD)
AML cells constitutively express the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO)^ref.
Classification : several types are distinguished, named according to the stage in which abnormal proliferation begins. The evolution of the classification system in AML from morphology to cytogenetic/genetic-based reflects the recognition of the importance of subtype-specific biology^ref.French-American-British (FAB) classification, 1976^ref (a classification of acute leukemia produced by a 3-nation joint collaboration based on cytomorphology and cytochemistry) directly relates to severity of prognosis :
• M0 : morphologically undistinguishable (look for rearrengement of BcR or TcR genes)

Laboratory examinations :
• cytomorphology :
• blasts > 20% of nucleated bone marrow cells
• blasts > 20% of nonerythroid (excluding also lymphocytes, plasma cells, macrophages and mast cells) bone marrow cells
• < 3% of blasts are positive for Sudan Black B or MPO at optic microscopy
• blasts recognized as myeloblasts through immunological markers or ultrastructural cytochemistry
• cytogenetics : significant association with high-risk cytogenetics and 11q23 abnormalities^ref. Trisomy 13 in a patient with unusual durable remission^ref
• immunophenotype :  CD13⁺33⁺34⁺, MPO⁺, HLA-DR⁺
• M1 (15-20%) :

Laboratory examinations :
• cytomorphology :
• blasts > 20% of bone marrow cells; poorly granular blasts
• blasts >= 90% of nonerythroid (excluding also lymphocytes, plasma cells, macrophages and mast cells) bone marrow cells
• > 3% of blasts positive for peroxidase or Sudan black B
• maturating bone marrow monocytes (from promonocyte to monocyte) < 10% of nonerythroid bone marrow cells
• maturating bone marrow granulocytes (from promyelocyte to PMN granulocyte) < 10% of nonerythroid cells
• cytogenetics : t(1;3)(p36;q21), inv(3)(q21;q26), ins(3;3)(q26;q21q26), t(3;3)(q21;q26), t(9;22)(q34;q11) or +11
• immunophenotype : CD11⁺13⁺33⁺19^+/- HLA-DR⁺
• M2 (25%) :
• M2 Baso / basophilic leukemia : a rare type of leukemia in which basophils predominate; both acute and chronic varieties have been observed. t(6;9) (p23;q33)
• M2 Eos ?
Laboratory examinations :
• cytomorphology :
• bone marrow blasts >= 20% of bone marrow cells; very granular blasts
• blasts 20-89% of nonerythroid bone marrow cells
• maturating bone marrow granulocytes (from promyelocyte to PMN granulocyte) > 10% of nonerythroid cells
• maturating bone marrow monocytes (from promonocyte to monocyte) < 20% of nonerythroid cells and lack of other criteria diagnostic of AML M4
• cytogenetics : +4, t(6;9)(p23;q34), t(7;11)(p15;p15), +8, t(8;21)(q22;q22) [=> AML1 / RUNX1/ETO], +9, t(9;22)(q34;q11), +11 or t(11;17)(q23;q25)
• immunophenotype : CD11⁺13⁺33⁺19^+/- HLA-DR⁺
• M3 / acute promyelocytic leukemia (PML) (APL) (8-12%)

Epidemiology : usually occurs in young adults.
Aetiology :
• de novo APL
• therapy-related APL (t-APL) develops usually less than 3 years after a primary neoplasm (especially breast carcinoma) treated in particular with DNA topoisomerase II inhibitors^ref (anthracyclines or mitoxantrone and less often etoposide^{ref1, ref2, ref3, ref4, ref5, ref6, ref7, ref8, ref9, ref10, ref11, ref12, ref13, ref14, ref15, ref16, ref17, ref18, ref19, ref20, ref21, ref22, ref23, ref24, ref25}). Characteristics and outcome of tAPL seem similar to those of de novo APL^ref. 3 cases of APL occurred during gefitinib treatment^ref
Pathogenesis : activation of RARa gene on chromosome 17q21

Retinoids may be key for myeloid differentiation. Vitamin A-deficient mice and humans were noted to have defects in hematopoiesis18,19 and retinoids can preferentially stimulate granulopoiesis^{ref1, ref2}. In the early 1980s, it was noted that retinoic acid (ATRA) could induce differentiation of myeloid cell lines such as HL60^ref and of primary cells from patients with APL^ref. The cloning of the RARs and other members of the nuclear receptor superfamily allowed for further detailed studies into the mechanism of action of ATRA. Among the genes encoding RARs^{ref1, ref2, ref3}, RARa is identified with myeloid development^{ref1, ref2, ref3}

• t(15;17)(q22;q11-q21) (90%) => PML/RARa fusion protein (90%)^{ref1, ref2, ref3, ref4, ref5, ref6, ref7}.


Pathogenesis : PML/RARa fusion protein is cleaved by neutrophil elastase (NE), which is encoded by the ELA2 gene, whose transcription is activated in early myeloid development and maximally expressed at the early promyelocyte stage. Cleavage creates a modified form of the protein that is important for initiation of this cancer^ref . PML-RARa recruits histone deacetylase (HDACs) (except for the AHT mutant) to ...
• ... chromatin to inhibit the expression of RAR target genes, predisposing cells to tumorigenesis
• ... p53 (whose mutations are surprisingly rare in APL) : deacetylated p53 is more susceptible to proteasomal degradation via MDM2^ref
APL shows both differentiation and proliferation defects.

Although both C/EBPa and C/EBPe can significantly prolong survival in a mouse model of APL, they are not functionally equivalent in this capacity. Forced expression of C/EBPa or C/EBPe in combination with ATRA treatment has a synergistic effect on survival of leukemic mice compared to either therapy alone^ref.
• t(11;17)(q23;q21) : fused to promyelocytic leukemia zinc finger (PLZF) gene (M3 V), which are retinoid-resistant. The PLZF/RARA cases were characterized by a predominance of blasts with regular nuclei, an increased number of Pelger-like cells, and by expression of CD56 in 4 of 6 cases tested. Use of this classification system, combined with an analysis for CD56 / NCAM1 expression, should allow early recognition of APL cases requiring tailored molecular investigations^ref.


• t(5;17)(q35;q21) : fused to nucleophosmin (NPM). Lacks Auer rods.


• t(11;17)(q13;q21) : fused to nuclear matrix associated (NuMA)


• t17q21 : STAT5B
PML oncogenic domains (PODs) / Kremer nuclear bodies / nuclear dots (ND10) (Ø 0.3÷0.5 mm; 10÷30 per nucleus ; made up of PML, Sp100, p53, pRb1, Daxx and BLM) disappear during APL. If cells are CD7⁺ => worse prognosis. While many promyelocyte-specific genes were highly expressed in all APL samples, 116 genes were reproducibly dysregulated in many independent APL samples, including Fos, Jun, Egr-1, TNF, and VCAM-1. However, this set of commonly dysregulated genes was expressed normally in preleukemic, early myeloid cells from mice expressing PML-RARa under control of the murine cathepsin G locus, suggesting that dysregulation occurs as a "downstream" event during disease progression^ref
Symptoms & signs : thrombocytopenia, hypofibrinogenemia => hemorrhages^ref; cutaneous promyelocytic sarcoma at sites of vascular access and marrow aspiration^ref. Around 10% of patients die in the presentation period as a consequence of the associated bleeding diathesis. The cause of the coagulopathy is complex resulting from a combination of tissue factor (TF) and cancer procoagulant (CP) induced activation of the coagulation cascade and the fibrinolytic system => disseminated intravascular coagulation (DIC), exaggerated fibrinolysis due predominantly to enhanced expression of annexin II on APL blast cell membranes^ref and blast cell production of cytokines. All-trans retinoic acid (ATRA) has revolutionised the treatment of APL. When combined with chemotherapy long term survival rates of up to 80% can be achieved. Commencement of ATRA induces APL blast cell differentiation and is associated with a rapid resolution of the bleeding tendency through a combination of effects which include up regulation of thrombomodulin and down regulation of TF and CP production and cell surface expression of annexin II.decreased levels of coagulation factor V
Laboratory examinations : there were no major differences observed in morphology or immunophenotype between cases with the classic t(15;17) and those with the cryptic PML/RARA gene rearrangements
• cytomorphology : morphology of blasts (hypergranular cells with many Auer rods)^{ref1, ref2}
• conventional karyotype (when normal it does not exclude the presence of rearrangements due to insertions or more complex mechanisms, including 3-way and simple variant translocations^ref), FISH, anti-PML PG-M3 mAb immunocytochemistry (directed against the amino terminal portion of the human PML gene product), change of the nuclear staining pattern from speckled ( due to localization of the wild-type PML protein into discrete dots (5 to 20 per nucleus), named PML nuclear bodies) to microgranular (PML-RARa fusion protein)^ref. Additional lesions have no prognostic value : FLT3 alterations are associated in APL with more aggressive clinical features but these lesions may not play a major role in leukemia progression^ref.
• immunophenotype : CD2^+/-10^-11c⁺13⁺14^-15⁺19⁺20^-33⁺34^+/-HLA-DR^-
Therapy^ref :

	all-trans retinoic acid (ATRA) inhibits PML/RARa hybrid protein, preventing HDACs from inhibiting transcription of differentiation genes and leading to recovery 70-80% of treated patients. Higher concentrations of ATRA are required to detach the HDAC complexref	chemotherapy
CR	96%	76%
48-mo OS	80%

• induction therapy : taken together, replacing standard chemotherapy with ATO in newly diagnosed APL will require larger studies. However, for selected patients who cannot tolerate anthracycline—for example those with cardiac dysfunction, older adults with poor performance status, and possibly Jehovah's Witnesses—ATO (probably still in combination with ATRA) would be a very reasonable alternative to the standard ATRA/chemotherapy. Of interest, in this report, patients were initially enrolled in the study because they could not afford standard therapy since the cost of single-agent ATO was much lower. In countries where cost would prohibit standard treatment of APL, a cheaper ATO, produced under good quality control, would be effective in curing many APL patients.
• single agent all-trans retinoic acid (ATRA) induces hematologic complete remission (CR) in almost all patients, but very often fails to produce molecular remissions. ATRA resolves the differentiation block in t(15;17) acute myeloid leukemia blasts by restoring PU.1 expression^ref, presumably through degradation of the PML-RARA fusion protein^ref
• all-trans retinoic acid (ATRA) + chemotherapy^ref :
• induction therapy : ATRA 45 mg/m² PO (divided into 2 doses) daily for 90 days or until complete remission (CR) + anthracycline^{ref1, ref2} :
• ATRA + idarubicin (AIDA) 12 mg/m² IV days 2, 4, 6, 8^ref or for 4 days beginning on day 5 of ATRA^ref
• ATRA + daunorubicin
As ATRA has few side effects, therapy should be initiated before genetic diagnosis to prevent hemorrhagic complications. Although many still employ cytarabine in the induction and postremission management of APL patients, its use is probably not necessary^ref. Finding positive myeloblasts at the of induction therapy doesn't justify salvage therapy. Add aggressive platelet transfusions, tranexamic acid and low-dose heparin to prevent hemorrhages. Past trials involved :
• daunorubicin alone^ref
• idarubicin alone^{ref1, ref2}
Induction toxicities (not graded) : fever (93%), bacteremia (22%), hemorrhage (67%), thrombocytopenia (19 days to recovery > 50,000). 12/123 deaths in induction. Neutropenia median days to recovery : 24. Emetogenic potential : days 2, 4, 6, 8 level 3.
• postremission or consolidation therapy (not generally thought effective in other AML subtypes) : 2 cycles including anthracyclines (intensity related to risk : WBC > 10,000, PLT > 40,000)
• low and intermediate risk :
• consolidation #1 : idarubicin 5 mg/m²/day IV days 1, 4 (grade 3-4 neutropenia : 28%). Emetogenic potential days 1-4 level 3
• consolidation #2 : mitoxantrone 10 mg/m²/day IV days 1-5 (grade 3-4 neutropenia : 94%). Emetogenic potential days 1-5 level 3
• consolidation #3 : idarubicin 12 mg/m² IV day 1 (grade 3-4 neutropenia : 17%). Emetogenic potential days 1 level 3
• high risk : ? + cytarabine + etoposide
• maintenance therapy for 2 years (not generally thought effective in other AML subtypes) : tretinoin 45 mg/m2/day days 1-15 (repeat every 3 months), methotrexate 15 mg/m2 IM every week, mercaptopurine 90 mg/m2/day PO daily. Anyway 15% relapse^ref. ATRA resistance is not explained by LBD mutations, so pharmacodynamic reasons are likely to exist.
Grade 3-4 toxicites : pulmonary (16%), oral (14%), ATRA syndrome (6% : definite; 20% : indeterminate), cardiac (6%), hepatic (5%), diarrhea (3%), dermatologic (2%), neurologic (2%), renal (1%).
• single-agent arsenic trioxide (ATO)^ref : a study from study China showed, using quantitative PCR, that the number of PML/RARa transcript copies was significantly lower after induction treatment with ATO than with ATRA in a small group of newly diagnosed patients^ref. Similar results were reported by a group in Iran^ref. ATO induced in 72 newly diagnosed patients a CR rate of 86% (although a minority of 8 patients received anthracycline for high white cell count), without evidence of disease resistance. Prior to the next treatment cycle, most (76%) of the studied CR patients were PCR negative for PML/RARa. However, of greater interest is that ATO alone, given as consolidation plus maintenance of 10 doses per month for 6 cycles, was very effective in maintaining the molecular remission. The 3-year EFS was 75%. Further, using the white cell and platelet count at diagnosis, Mathews et al identified 2 risk groups that are different from those reported by Sanz et al^ref. All 20 patients in the good-risk group were alive and in remission^ref. Although this approach is less toxic and the results are promising, single-agent ATO cannot yet be considered an alternative to well-studied standard APL treatment: the number of patients is much smaller and the duration of follow-up is relatively shorter than those studied with ATRA plus chemotherapy. Also, the outcome of those not considered good-risk patients may not be as positive as in the poor- and intermediate-risk patients classified by the criteria of Sanz et al^ref despite the difficulty in a direct comparison. An advantage of single-agent ATO was its limited toxicity, especially infrequent and very short occurrence of grade  neutropenia. However, this is probably gained by eliminating the intensive chemotherapy, raising the question of whether ATRA also needs to be avoided. One might be concerned with using a single agent in a disease that is already highly curable
• arsenic trioxide (ATO) + all-trans retinoic acid (ATRA) : synergism was demonstrated in APL animal models. Further, in newly diagnosed APL patients, MRD measured by quantitative PCR was significantly lower with ATRA + ATO induction than with ATO alone^ref. A smaller study showed a very high percentage of continued molecular remission even in high-risk patients with ATRA plus ATO, with the addition of gemtuzumab only for high-risk patients^ref
• all-trans retinoic acid (ATRA) + chemotherapy + arsenic trioxide (ATO) : a small randomized trial from China suggested that the combination of all 3 modalities—chemotherapy, ATRA, and ATO in different treatment phases—resulted in significantly better outcome than chemotherapy + ATRA^ref. A much larger U.S. intergroup randomized trial at MD Anderson studied whether adding 2 cycles of ATO consolidations to standard ATRA/chemotherapy would improve the overall outcome, but the results are pending.
• relapsed APL :
• single-agent arsenic trioxide (ATO) (Fowler's solution) is more efficient than ATRA in reducing the degree of minimal residual APL cells and induces molecular remissions in almost all patients^ref : leads to a 4-log reduction in the APL disease burden in heavily pre-treated patients and is now being evaluated to consolidate first remissions
• induction therapy : ATO 0.15 mg/kg/day IV over 2 hours daily; cumulative maximum of 60 doses.
• consolidation therapy : ATO 0.15 mg/kg/day IV over 2 hours 5 days per week; cumulative maximum of 25 doses
Grade 3-4 neutropenia (8%), coagulopathy (clinical : 48%; subclinical : 35%), APL syndrome (25%), grade 4 hyperglycemia (13%), grade 4 hyperkalemia (13%), grade 4 dyspnea (10%), grade 4 abdominal pain (8%), grade 4 headache (3%), grade 4 insomnia (3%), grade 3 neuropathy (3%) => 40% had at least 1 EKG with QT prolongation, acute renal failure occurred in 3 patients. Monitor for signs of the APL differentiation syndrome (ATRA syndrome). Baseline EKG should be performed. Monitor the QTc interval. Monitor the patients for signs and symptoms of arsenic toxicity; recommended antidotes include dimercaprol and penicillamine, leukocytosis (50%). Emetogenic potential level 3^ref
• anti-CD33 immunotoxin conjugate (gemtuzumab ozogamicin) (Mylotarg^®) : 40% of patients remain positive but have no increase relapse risk. Mylotarg + ATO in second remission patients would be an interesting pilot study.
• allogeneic HSCT is not recommended after the first remission, but only in patients not undergoing molecular remission using a poorly sensitive PCR assay after consolidation therapy
• therapeutic DNA cancer vaccine using PML/RARa as a TSA fused with the highly immunogenic tetanus toxoid fragment C gene (FrC) is as effective as ATRA and when the 2 therapeutics are combined mice can live 40% longer than with either treatment alone^ref
Follow-up :
• bone marrow aspiration biopsy every 3 months
• molecular monitoring : APL is the one subtype of AML in which it has proven useful after achievement of complete response (CR). Few patients who achieve PCR^- status after postremission chemotherapy relapse; whereas those with persistently detectable PML-RAR fusion transcripts have a 25% risk of relapse^ref, yet whether such relapses can be prevented with additional therapy remains unclear
Prognosis : while the cure rate in APL with "standard" therapy is favorable (60-70%), the problems of t-MDS^ref and late central nervous system (CNS) relapses^ref have recently been described. Sanz criteria^ref :
• low-risk (WBC count <= 10,000/ml, platelet count > 40 × 10⁹/L)
• intermediate-risk (WBC count <= 10,000/ml, platelets  40 × 10⁹/L)
• high-risk (WBC count > 10,000/ml)
• M4 / acute myelomonocytic leukemia / Naegeli's leukemia (25%) : both malignant monocytes (> 20%) and myeloblasts. Its chronic counterpart is considered a MDS/MPD (chronic myelomonocytic leukemia). Methicillin-resistant coagulase-negative Staphylococcus have been identified within neutrophils^ref

Epidemiology : usually affects middle aged to older adults.
• M4 Eo : inv(16)(p13;q22), t(16;16)(p13;p22) or del(16)(q22) => fusion protein CBFB-smooth muscle myosin heavy chain (SMMHC) / MYH11 in which the CBFß transcription factor is fused to the tail domain of a smooth muscle myosin heavy chain.
Laboratory examinations :
• cytomorphology :
• blasts >= 20% of bone marrow cells
• blasts >= 20% of nonerythroid bone marrow cells
• maturating bone marrow granulocytes (from myeloblasts to PMN granulocytes) >= 20% of nonerythoid cells
• significant monocyte component as seen by one of the following criteria :
• bone marrow monocyte component (from monoblast to monocyte) >= 20% of nonerythroid cells and peripheral blood monocyte component > 5 x 10⁹/l OR
• bone marrow monocyte component (from monoblast to monocyte) >= 20% of nonerythroid cells, confirmed by cytochemistry or increase in lysozyme concentration in serum or urine OR
• bone marrow as in AML M2 but monocyte component in peripheral blood > 5 x 10⁹/l  and confirmation by cytochemistry or increase in lysozyme concentration in serum or urine
• cytogenetics : t(1;3)(p36;q21), t(1;7)(q10;p10), t(1;11)(q21;q23), inv(3)(q21;q26), ins(3;3)(q26;q21q26), t(3;3)(q21;q26), +4, t(6;9)(p23;q34), t(6;11)(q27;q23), +8, +9, +11, t(11;17)(q23;q25), t(11;19)(q23;p23) or +22
• immunophenotype : CD10^-11⁺13⁺14⁺15⁺20^-32⁺33⁺68⁺ HLA-DR⁺
Variants :
• M4 with cytophagocytosis
• M5 / acute monocytic (or monoblastic) leukemia / Schilling's leukemia / histiocytic leukemia (10%) : the predominating cells are identified as monocytes. A few myelocytes may be present, but not as many as in acute myelomonocytic leukemia.

Epidemiology : can affect any age group
Symptoms & signs : extramedullary localizations
Laboratory examinations :
• cytomorphology :
• blasts >= 20% of bone marrow cells
• blasts >= 20% of nonerythroid bone marrow cells
• bone marrow monocyte component >= 80% of nonerythroid cells
• M5a or undifferentiated (t(9;11)(p21-22;q23) or t/del(11q23)): monoblast > 80 % of all cells in monocytic lineage
• M5b or differentiated (t(8;16)(p11;p13)): monoblast < 80 % of all cells in monocytic lineage
• cytogenetics : t(1;11)(q21;q23), t(6;11)(q27;q23), +8, +9, t(10;11)(p11-15;q13-23), t(11;17)(q23;q25), t(11;19)(q23;p23); mucosal infiltrations. Trisomy 22 as sole cytogenetic abnormality in M5b^ref
• immunophenotype : CD10^-11⁺13⁺14⁺20^-33⁺68⁺ HLA-DR⁺
Variants :
• M5 with cytophagocytosis (mainly erythrophagocytosis)
• M5c (?) with circulating macrophage-like cells
• myelodendritic acute leukemia
• M6 / erythroleukemia / Di Guglielmo syndrome (DG syndrome) : n oligoblastic proliferation of both erythroid and myeloid precursors described firstly by Copelli in 1912 (Copelli M. Di una emoptia sistemizzata rappresentata da una iperplasia eritroblastica eritromatosi. Pathologica 4:460-465 (1912)). Di Guglielmo named it erythroleukemia (Di Guglielmo G. Ricerche di ematologia. Folia Medica 3:386-396 (1917)) and Dameshek proposed the name DG-syndrome. It is the acute counterpart of polycythemia vera

The erythroleukemia developed by spi-1/PU.1 transgenic mice is a multistage process characterized by an early arrest of the proerythroblast differentiation followed later on by malignant transformation. Acquired mutations in the SCF receptor gene (Kit) occur in 86% of tumors isolated during the late stage of the disease. Kit mutations affect codon 814 or 818. Ectopic expression of Kit mutants in nonmalignant proerythroblasts confers erythropoietin independence and tumorigenicity to cells. Using PP1, PP2, and imatinib mesylate, Kit mutants are responsible for the autonomous expansion of malignant cells via Erk1/2 and PI3K/Akt activations^ref.
Laboratory examinations :
• cytomorphology :
• erythroblasts > 50% of nucleated bone marrow cells

AND
• blasts >= 30% of nonerythroid bone marrow cells
• immunophenotype : CD10^-20^- HLA-DR⁺ glycophorin⁺ spectrin⁺ ABH antigens⁺ carbonic anhydrase I⁺
• cytogenetics : inv(3)(q21;q26), ins(3;3)(q26;q21q26),  t(3;3)(q21;q26) or t(3;5)(q21-25;q31-35)
• M7 / acute megakaryocytic (or megakaryoblastic) leukemia (AMKL) :

Epidemiology : can affect any age group
Risk factor : Down's syndrome (overexpression of a gene on chromosome 21 might stimulate abnormal proliferation of HSC, which would then be able to acquire mutations, among which GATA-1 on X chromosome)
Laboratory examinations :
• thrombocytosis
• punctio sicca or bone marrow fibrosis
• cytomorphology :
• blasts >= 30% of nucleated bone marrow cells
• blasts recognized as megakaryoblasts by immunophenotype, ultrastructural or cytochemistry
• cytogenetics : t(1;22)(p13;q13)
• immunophenotype : CD10^-20^-34⁺41⁺42a⁺42b⁺61⁺vWF⁺ HLA-DR⁺
• Rieder's cell leukemia : a form of AML in which the blood contains Rieder's cells, asynchronously developed lymphocytes that have immature cytoplasm and a lobulated, indented, comparatively more mature nucleus.

Laboratory examinations : Rieder's cell or lymphocyte (a myeloblast whose nucleus with wide and deep indentations suggesting lobulation, which may represent asynchronism of nuclear and cytoplasmic maturation)
• mixed lineage leukemias
• acute undifferentiated leukemia (AUL) / stem cell leukemia / blast cell leukemia / hemoblastic leukemia / hemocytoblastic leukemia / undifferentiated cell leukemia : predominating cell is so immature and primitive that it cannot be classified

Laboratory examinations :
• immunophenotype : CD7⁺13^-33^-34⁺45⁺HLA-DR⁺TdT⁺
• cytochemistry : negative SBB, MPO, esterase and PAS
• acute myeloblastic leukemia : a common kind of AML, in which myeloblasts predominate

Epidemiology : it usually occurs in infants and middle-aged to older adults. 2 types are distinguished :
• those that have minimal cell differentiation or maturation
• those that have more advanced differentiation.
Symptoms & signs : Mosler's sign (sternal tenderness in acute myeloblastic leukemia)
Laboratory examinations :
• myeloblastemia : the presence of myeloblasts in the blood, as in AML
• myeloblastosis : the presence of an excess of myeloblasts in the blood, as in AML
• micromyeloblastic leukemia : a form of myelogenous leukemia in which the immature, nucleoli-containing cells are small and are distinguishable from lymphocytes only by supravital staining.
• transient myeloproliferative disorder (TMD) / transient leukemia (TL) occurs in 10% of patients with Down syndrome

Laboratory examinations : pancytopenia, hepatosplenomegaly, and circulating immature WBCs
Prognosis : although most cases of TMD resolve without therapy in 1 to 3 months ( by 1 year of age), data suggest that true acute leukemia may develop in 20-30% of patients with TMD. There is an increased risk of leukemia with an equal incidence of lymphoid and myeloid leukemia. AML-M7 / acute megakaryocytic leukemia (AMKL) is the most common form of acute myeloid leukemia (AML) in this setting, and is uncommon in children without DS. Somatic mutations of the gene encoding the hematopoetic growth factor GATA1 have been shown to be specific for TMD and AMKL in children with DS. Myelodysplastic syndrome can precede AML. Although the risk for leukemia is higher in individuals with DS, these patients have a lower risk of developing solid tumors, with the exception of germ cell tumors, and perhaps retinoblastoma and lymphoma^ref. A prospective Children's Oncology Group (COG) study by Massey and colleagues of 47 patients with Down syndrome with a diagnosis of transient leukemia (more commonly known as transient myeloproliferative disorder) revealed early deaths in 8 patients due to liver failure and disseminated intravascular coagulation, and the subsequent development of acute megakaryoblastic leukemia in 8 patients and B-cell–precursor ALL in another patient at a mean of 20 months from diagnosis. As one might expect from past reports^ref, all but one of these patients, a child with acute megakaryoblastic leukemia, responded well to chemotherapy and remained in continuous complete remission. Early death was associated with a high presenting leukocyte count, increased levels of bilirubin and hepatic enzymes, and failure to regain normal blood counts. By contrast, the presenting leukocyte count, blast cell percentage, and time to clearance of blasts or normalization of blood counts did not predict the emergence of frank leukemia. The presence of karyotypic abnormalities in addition to trisomy 21 was only weakly correlated with leukemia development; that is, 4 of 7 such patients, compared with 5 of 35 lacking additional karyotypic abnormalities, subsequently developed leukemia. Interestingly, patients with overt leukemia were less likely than the unaffected group to be symptomatic at diagnosis of transient leukemia (one of 9 patients vs 26 of 39 patients). The COG study was not intended to evaluate therapy, so patients were treated according to the discretion of their physicians. Only one child received standard AML therapy, and 2 patients got low doses of cytarabine shortly after diagnosis. All three of these patients remained well. Two additional patients received low-dose cytarabine for progressive symptoms and died 1 or 2 days later. On the strength of those observations and limited experience by others,4 the authors recommend early use of low-dose cytarabine as prophylactic chemotherapy in patients with progressive organomegaly and evidence of liver dysfunction or in boys with cytogenetic abnormalities other than trisomy 21. However, for a prospective trial of low-dose cytarabine in all Down syndrome patients with transient leukemia because of the lack of factors that can be used with certainty to predict leukemia development or early death. Indeed, as mentioned, asymptomatic patients were more likely than symptomatic patients to develop leukemia. While 6 of 7 boys with additional cytogenetic abnormalities had a subsequent adverse event (4 leukemias and 2 early deaths), 3 of the remaining 22 boys also converted to overt leukemia, and 4 died early. Finally, low-dose cytarabine appears to be an effective and relatively nontoxic agent in infants with Down syndrome and transient leukemia^ref. It should be emphasized that the true incidence of transient leukemia is currently unknown, since blood counts are not routinely performed in Down syndrome patients. Conceivably, some of these leukemias resolve permanently without being diagnosed in the first place. Thus, an immediate challenge is to learn the exact prevalence and history of this disorder by prospectively studying all neonates with Down syndrome^ref.
Therapy : children with DS and leukemia are more sensitive to some chemotherapeutic agents such as methotrexate than other children which requires careful monitoring for toxicity.
WHO classification, 2001 : during the nearly 3 decades that the FAB system was used for classifying AML, it was discovered that many cases of AML are associated with recurring genetic abnormalities that affect cellular pathways of myeloid maturation and proliferation. The FAB classification provided a consistent morphologic and cytochemical framework in which the significance of the genetic lesions could be appreciated. In some instances, such as APL and acute myelomonocytic leukemia with abnormal eosinophils (M4Eo), the morphologic characteristics predict the genetic abnormalities. However, morphologic-genetic correlations are not always perfect, and the genetic findings may predict the prognosis and biologic properties of the leukemia more consistently than does morphology. Furthermore, in many cases either there is no correlation between morphology and genetic defects or the underlying genetic and molecular defects cannot be identified. Thus, although the FAB classification recognizes the morphologic heterogeneity of AML, it does not always reflect the genetic or clinical diversity of the disease. Some investigators suggest that a more relevant classification of AML can be achieved if 2 distinctive subgroups with different biologic features are recognized:
• AML that evolves from MDS or has features similar to those found in MDS
• AML that arises de novo without significant myelodysplastic features^{ref1, ref2}
The characteristics associated with these 2 groups indicate that they have fundamentally different mechanisms of leukemogenesis. MDS-related leukemia is associated with multilineage dysplasia, poor-risk cytogenetic findings that often include loss of genetic material, and a poor response to therapy. The incidence of this type increases with age, consistent with the hypothesis that MDS and MDS-related leukemia arise through multiple insults to the genetic constitution of the hematopoietic stem cell that occur over time. In contrast, de novo AML usually lacks significant multilineage dysplasia, is often associated with good-risk cytogenetic abnormalities, particularly certain recurring chromosomal translocations and inversions, and often has a favorable response to appropriate therapy, with good failure-free and overall survival times^{ref1, ref2}. This type of leukemia has a relatively constant incidence throughout life and is the type most likely to be observed in children and young adults^ref. It is probable that specific genetic events associated with these leukemias, which often involve transcription factors, are a major, rate-limiting step in their pathogenesis^ref. The concept that these and other subgroups of AML can be recognized and classified as unique diseases through correlation of morphologic, genetic, and clinical data is a major theme of the WHO classification and serves as the basis for the 2 most significant differences between it and the FAB classification: (1) a lower blast threshold for the diagnosis of AML in the WHO classification and (2) the categorization of cases of AML into unique clinical and biologic subgroups in the WHO classification. In the WHO classification, the blast threshold for the diagnosis of AML is reduced from 30% to 20% blasts in the blood or marrow. In addition, patients with the clonal, recurring cytogenetic abnormalities t(8;21)(q22;q22), inv(16)(p13q22) or t(16;16)(p13;q22), and t(15;17)(q22;q12) should be considered to have AML regardless of the blast percentage. A number of studies indicate that patients with 20% to 29% blasts in their blood or bone marrow often have similar clinical featuresincluding response to therapy and survival times as those with 30% or more blasts. According to the FAB criteria for MDS, patients with 20% to 29% blasts in the blood or marrow are classified in the MDS subgroup of refractory anemia with excess of blasts in transformation (RAEBT)^ref. In the WHO proposal, most patients with 20% to 29% blasts and myelodysplasia will be classified as AML with multilineage dysplasiaa subgroup that includes patients with a prior history of MDS as well as patients who present initially with AML and dysplasia in multiple cell lines. AML with multilineage dysplasia can be considered the most advanced manifestation of MDS. Numerous reports indicate that a significant number of patients with RAEBT and AML with myelodysplastic-related features share several important biologic and clinical features. According to some studies, myeloid cells from patients with RAEBT and MDS-related AML have nearly identical profiles of proliferation and apoptosis that differ from those in refractory anemia (RA), refractory anemia with ringed sideroblasts (RARS), and refractory anemia with excess blasts (RAEB)^ref. Poor-risk cytogenetic abnormalities, including abnormalities of chromosome 7 and complex abnormalities, increased expression of multidrug-resistance glycoproteins, and poor response to chemotherapy, are also common in RAEBT and in MDS-related AML^{ref1, ref2}. Some investigators have also reported that, when matched for similar disease features, such as white blood cell count or cytogenetic abnormalities, patients with RAEBT and AML have similar survival times if treated with identical therapy^{ref1, ref2, ref3}. In addition, data from the International MDS Risk Analysis Workshop indicate that RAEBT is not an indolent disease. In that study, 25% of patients with 20% to 30% blasts evolved to AML in 2 to 3 months, 50% in 3 months, and > 60% developed AML within 1 year. The median survival time for patients with RAEBT was less than 1 year^ref. The sum of these data indicates that patients with 20% to 29% blasts in the blood and/or bone marrow accompanied by multilineage myelodysplasia have essentially the same disease as do those with AML with multilineage dysplasia and 30% or more blasts and should be classified in the same category. It is important to emphasize that therapeutic decisions for patients with MDS-related AML should be based not only on the percentage of blasts but also on clinical findings, the rate of disease progression, and genetic data. The effect on the blast percentage of any previous therapy, such as growth factor therapy, must also be taken into account. These cautionary notes apply regardless of whether the blast count is 20%, 30%, or more in a patient with myelodysplastic-related disease. The lower blast percentage required for a diagnosis of AML also addresses another issue: the classification of patients who have no evidence of multilineage myelodysplasiathat is, patients with true de novo AMLas RAEBT because their blood or bone marrow specimens have fewer than 30% blasts on the initial evaluation. If the leukemia manifests no evidence that it is myelodysplastic related, it does not seem justified to categorize it as a myelodysplastic syndrome. Such a designation could result in inappropriate stratification for risk-determined therapy. Patients with the specific recurring cytogenetic abnormalities t(8;21)(q22;q22), inv(16)(p13q22) or t(16;16)(p13;q22), and t(15;17)(q22;q12) should be classified as having AML regardless of the blast percentage.
• acute myeloid leukemia with recurrent genetic abnormalities (30%^{ref1, ref2, ref3}) : in cases of AML with t(15;17), t(8;21), and inv(16) or t(16;16), there is such a strong correlation between the genetic findings and the morphology that the genetic abnormality can usually be predicted from the microscopic evaluation of the blood and marrow specimens. Furthermore, because AMLs associated with these abnormalities have distinctive clinical findings and a favorable response to appropriate therapy, they can be considered as truly distinct clinicopathologicgenetic entities^{ref1, ref2, ref3, ref4}. Although abnormalities of 11q23 are often associated with myelomonocytic or monocytic differentiation, AML associated with this abnormality cannot always be predicted with any degree of confidence from the morphology alone. The leukemias associated with these recurrent genetic abnormalities generally have the features of de novo AML. However, all of the genes affected in this group are apparently vulnerable to damage caused by certain types of chemotherapy, specifically with topoisomerase II inhibitors, and can be involved in some cases of therapy-related leukemia^{ref1, ref2}. In these instances, the unique clinical background indicates that the case should be classified as therapy-related AML. It is anticipated that the list of entities included in this subgroup will expand in the future. Some members of the WHO committees suggested that other recurring genetic abnormalities, such as t(8;16), t(6;9), or t(3;3), should be included in the current listing. Although these latter genetic abnormalities are often associated with unique morphologic and/or clinical features, it is not yet clear whether they define a unique disease or are mainly of prognostic significance within other subgroups. Furthermore, at least some of the recurring genetic abnormalities (for example, t(3;3)) are more frequently associated with myelodysplastic-related disease than with de novo AML and would be better incorporated into the subgroup of AML with multilineage dysplasia. It has been suggested that the WHO classification cannot realistically be used for AML because genetic information is not always available in a timely manner^ref. Alternatively, a "realistic" classification has been proposed that permits cases to be classified if the morphologic findings are "suggestive" of a specific genetic abnormality even without adequate knowledge that such a genetic defect is actually present