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NCI/PDQ^® Health professionals: Childhood Acute Myeloid Leukemia/Other Myeloid Malignancies Treatment (PDQ®)

National Cancer Institute
Last Modified: November 21, 2012

TABLE OF CONTENTS

• General Information
  • Myeloid Leukemias in Children

• Classification of Pediatric Myeloid Malignancies
  • French-American-British (FAB) Classification for Childhood Acute Myeloid Leukemia
  • World Health Organization (WHO) Classification System
  • Histochemical Evaluation
  • Immunophenotypic Evaluation
  • Cytogenetic Evaluation and Molecular Abnormalities
  • Classification of Myelodysplastic Syndromes in Children
  • Diagnostic Classification of Juvenile Myelomonocytic Leukemia

• Stage Information
  • Newly Diagnosed
  • Remission

• Treatment Overview for Acute Myeloid Leukemia (AML)
  • Prognostic Factors in Childhood AML
    • Risk classification systems under clinical evaluation

• Treatment of Newly Diagnosed AML
  • Induction Chemotherapy
    • Treatment options under clinical evaluation
  • Central Nervous System (CNS) Prophylaxis for AML
  • Granulocytic Sarcoma/Chloroma
  • Current Clinical Trials

• Postremission Therapy for AML
  • Treatment Options Under Clinical Evaluation
  • Current Clinical Trials

• Acute Promyelocytic Leukemia
  • Molecular Variants of APL Other than PML-RARA
  • Treatment Options Under Clinical Evaluation
  • Current Clinical Trials

• Children with Down Syndrome

• Myelodysplastic Syndromes
  • Treatment Options Under Clinical Evaluation
  • Current Clinical Trials

• Juvenile Myelomonocytic Leukemia
  • Current Clinical Trials

• Chronic Myelogenous Leukemia
  • Treatment of CML in Adults with TKIs
  • Treatment of CML in Children
  • Treatment Options Under Clinical Evaluation
  • Current Clinical Trials

• Recurrent Childhood AML and Other Myeloid Malignancies
  • Isolated CNS Relapse
  • Recurrent Acute Promyelocytic Leukemia (APL)
  • Current Clinical Trials

• Survivorship and Adverse Late Sequelae

• Changes to This Summary (11/21/2012)

• About This PDQ® Summary
  • Purpose of This Summary
  • Reviewers and Updates
  • Levels of Evidence
  • Permission to Use This Summary
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General Information

Back Up

Fortunately, cancer in children and adolescents is rare, although the overall incidence of childhood cancer has been slowly increasing since 1975. 1 Children and adolescents with cancer should be referred to medical centers that have a multidisciplinary team of cancer specialists with experience treating the cancers that occur during childhood and adolescence. This multidisciplinary team approach incorporates the skills of the primary care physician, pediatric surgical subspecialists, radiation oncologists, pediatric medical oncologists/hematologists, rehabilitation specialists, pediatric nurse specialists, social workers, and others in order to ensure that children receive treatment, supportive care, and rehabilitation that will achieve optimal survival and quality of life. (Refer to the PDQ® Supportive and Palliative Care summaries for specific information about supportive care for children and adolescents with cancer.)

Guidelines for pediatric cancer centers and their role in the treatment of children with cancer have been outlined by the American Academy of Pediatrics. 2 At these pediatric cancer centers, clinical trials are available for most types of cancer that occur in children and adolescents, and the opportunity to participate in these trials is offered to most patients/families. Clinical trials for children and adolescents with cancer are generally designed to compare potentially better therapy with therapy that is currently accepted as standard. Most of the progress made in identifying curative therapies for childhood cancers has been achieved through clinical trials. Information about ongoing clinical trials is available from the NCI Web site.

Dramatic improvements in survival have been achieved for children and adolescents with cancer. 1 Between 1975 and 2002, childhood cancer mortality has decreased by more than 50%. For acute myeloid leukemia, the 5-year survival rate has increased over the same time from less than 20% to 58% for children younger than 15 years and from less than 20% to approximately 40% for adolescents aged 15 to 19 years. 1 Childhood and adolescent cancer survivors require close follow-up because cancer therapy side effects may persist or develop months or years after treatment. (Refer to the PDQ® summary on Late Effects of Treatment for Childhood Cancer for specific information about the incidence, type, and monitoring of late effects in childhood and adolescent cancer survivors.)

Myeloid Leukemias in Children

Approximately 20% of childhood leukemias are of myeloid origin and they represent a spectrum of hematopoietic malignancies. 3 The majority of myeloid leukemias are acute and the remainder include chronic and/or subacute myeloproliferative disorders such as chronic myelogenous leukemia (CML) and juvenile myelomonocytic leukemia (JMML), as well as myelodysplastic syndromes.

Acute myeloid leukemia (AML) is defined as a clonal disorder caused by malignant transformation of a bone marrow-derived, self-renewing stem cell or progenitor, which demonstrates a decreased rate of self-destruction as well as aberrant differentiation. These events lead to increased accumulation in the bone marrow and other organs by these malignant myeloid cells. To be called acute, the bone marrow usually must include greater than 20% leukemic blasts, with some exceptions as noted in subsequent sections.

CML represents the most common of the chronic myeloproliferative disorders in childhood, although it accounts for only 10% to 15% of childhood myeloid leukemia. 3 Although CML has been diagnosed in very young children, most patients are aged 6 years and older. CML is a clonal panmyelopathy that involves all hematopoietic cell lineages. While the white blood cell (WBC) count can be extremely elevated, the bone marrow does not show increased numbers of leukemic blasts during the chronic phase of this disease. CML is nearly always characterized by the presence of the Philadelphia chromosome, a translocation between chromosomes 9 and 22 (i.e., t(9;22)) resulting in fusion of the BCR and ABL genes. Other chronic myeloproliferative syndromes, such as polycythemia vera and essential thrombocytosis, are extremely rare in children.

JMML represents the most common myeloproliferative syndrome observed in young children. JMML occurs at a median age of 1.8 years and characteristically presents with hepatosplenomegaly, lymphadenopathy, fever, and skin rash along with an elevated WBC count and increased circulating monocytes. 4 In addition, patients often have an elevated hemoglobin F, hypersensitivity of the leukemic cells to granulocyte-macrophage colony-stimulating factor (GM-CSF), monosomy 7, and leukemia cell mutations in a gene involved in RAS pathway signaling (e.g., NF1, KRAS/NRAS, PTPN11, or CBL). 4 5

The transient myeloproliferative disorder (TMD) (also termed transient leukemia) observed in infants with Down syndrome represents a clonal expansion of myeloblasts that can be difficult to distinguish from AML. Most importantly, TMD spontaneously regresses in most cases within the first 3 months of life. TMD blasts most commonly have megakaryoblastic differentiation characteristics and distinctive mutations involving the GATA1 gene. 6 7 TMD may occur in phenotypically normal infants with genetic mosaicism in the bone marrow for trisomy 21. While TMD is generally not characterized by cytogenetic abnormalities other than trisomy 21, the presence of additional cytogenetic findings may predict an increased risk for developing subsequent AML. 8 Approximately 20% of infants with Down syndrome and TMD eventually develop AML, with most cases diagnosed within the first 3 years of life. 7 8 Early death from TMD-related complications occurs in 10% to 20% of affected children. 8 9 Infants with progressive organomegaly, visceral effusions, and laboratory evidence of progressive liver dysfunction are at a particularly high risk for early mortality. 8

The myelodysplastic syndromes in children represent a heterogeneous group of disorders characterized by ineffective hematopoiesis, impaired maturation of myeloid progenitors with dysplastic morphologic features, and cytopenias. Although the majority of patients have normocellular or hypercellular bone marrows without increased numbers of leukemic blasts, some patients may present with a very hypocellular bone marrow, making the distinction between severe aplastic anemia and low-blast count AML difficult.

There are genetic risks associated with the development of AML. There is a high concordance rate of AML in identical twins, which is believed to be in large part a result of shared circulation and the inability of one twin to reject leukemic cells from the other twin during fetal development. 10 11 12 There is an estimated twofold to fourfold risk of fraternal twins both developing leukemia up to about age 6 years, after which the risk is not significantly greater than that of the general population. 13 14 The development of AML has also been associated with a variety of predisposition syndromes that result from chromosomal imbalances or instabilities, defects in DNA repair, altered cytokine receptor or signal transduction pathway activation, as well as altered protein synthesis. (Refer to the following list of inherited and acquired genetic syndromes associated with myeloid malignancies.)

Inherited and Acquired Genetic Syndromes Associated with Myeloid Malignancies
• Inherited syndromes
  • Chromosomal imbalances:
    • Down syndrome.
    • Familial monosomy 7 syndrome.

  • Chromosomal instability syndromes:
    • Fanconi anemia.
    • Dyskeratosis congenita.
    • Bloom syndrome.

  • Syndromes of growth and cell survival signaling pathway defects:
    • Neurofibromatosis type 1 (particularly JMML development).
    • Noonan syndrome (particularly JMML development).
    • Severe congenital neutropenia (Kostmann syndrome).
    • Shwachman-Diamond syndrome.
    • Diamond-Blackfan anemia.
    • Familial platelet disorder with a propensity to develop AML.
    • Congenital amegakaryocytic thrombocytopenia.
    • CBL germline syndrome (particularly in JMML).

• Acquired syndromes
  • Severe aplastic anemia.
  • Paroxysmal nocturnal hemoglobinuria.
  • Amegakaryocytic thrombocytopenia.
  • Acquired monosomy 7.

References:

1. Smith MA, Seibel NL, Altekruse SF, et al.: Outcomes for children and adolescents with cancer: challenges for the twenty-first century. J Clin Oncol 28 (15): 2625-34, 2010. [PUBMED Abstract]
2. Guidelines for the pediatric cancer center and role of such centers in diagnosis and treatment. American Academy of Pediatrics Section Statement Section on Hematology/Oncology. Pediatrics 99 (1): 139-41, 1997. [PUBMED Abstract]
3. Smith MA, Ries LA, Gurney JG, et al.: Leukemia. In: Ries LA, Smith MA, Gurney JG, et al., eds.: Cancer incidence and survival among children and adolescents: United States SEER Program 1975-1995. Bethesda, Md: National Cancer Institute, SEER Program, 1999. NIH Pub.No. 99-4649., pp 17-34. Also available online [PUBMED Abstract]
4. Niemeyer CM, Arico M, Basso G, et al.: Chronic myelomonocytic leukemia in childhood: a retrospective analysis of 110 cases. European Working Group on Myelodysplastic Syndromes in Childhood (EWOG-MDS) Blood 89 (10): 3534-43, 1997. [PUBMED Abstract]
5. Loh ML: Recent advances in the pathogenesis and treatment of juvenile myelomonocytic leukaemia. Br J Haematol 152 (6): 677-87, 2011. [PUBMED Abstract]
6. Hitzler JK, Cheung J, Li Y, et al.: GATA1 mutations in transient leukemia and acute megakaryoblastic leukemia of Down syndrome. Blood 101 (11): 4301-4, 2003. [PUBMED Abstract]
7. Mundschau G, Gurbuxani S, Gamis AS, et al.: Mutagenesis of GATA1 is an initiating event in Down syndrome leukemogenesis. Blood 101 (11): 4298-300, 2003. [PUBMED Abstract]
8. Massey GV, Zipursky A, Chang MN, et al.: A prospective study of the natural history of transient leukemia (TL) in neonates with Down syndrome (DS): Children's Oncology Group (COG) study POG-9481. Blood 107 (12): 4606-13, 2006. [PUBMED Abstract]
9. Homans AC, Verissimo AM, Vlacha V: Transient abnormal myelopoiesis of infancy associated with trisomy 21. Am J Pediatr Hematol Oncol 15 (4): 392-9, 1993. [PUBMED Abstract]
10. Zuelzer WW, Cox DE: Genetic aspects of leukemia. Semin Hematol 6 (3): 228-49, 1969. [PUBMED Abstract]
11. Miller RW: Persons with exceptionally high risk of leukemia. Cancer Res 27 (12): 2420-3, 1967. [PUBMED Abstract]
12. Inskip PD, Harvey EB, Boice JD Jr, et al.: Incidence of childhood cancer in twins. Cancer Causes Control 2 (5): 315-24, 1991. [PUBMED Abstract]
13. Kurita S, Kamei Y, Ota K: Genetic studies on familial leukemia. Cancer 34 (4): 1098-101, 1974. [PUBMED Abstract]
14. Greaves M: Pre-natal origins of childhood leukemia. Rev Clin Exp Hematol 7 (3): 233-45, 2003. [PUBMED Abstract]

Classification of Pediatric Myeloid Malignancies

Back Up

French-American-British (FAB) Classification for Childhood Acute Myeloid Leukemia

The first comprehensive morphologic-histochemical classification system for acute myeloid leukemia (AML) was developed by the FAB Cooperative Group. 1 2 3 4 5 This classification system categorizes AML into the following major subtypes primarily based on morphology and immunohistochemical detection of lineage markers:

• M0: acute myeloblastic leukemia without differentiation. 6 7 [Note: M0 AML, also referred to as minimally differentiated AML, does not express myeloperoxidase (MPO) at the light microscopy level, but may show characteristic granules by electron microscopy. M0 AML can be defined by expression of cluster determinant (CD) markers such as CD13, CD33, and CD117 (c-KIT) in the absence of lymphoid differentiation. To be categorized as M0, the leukemic blasts must not display specific morphologic or histochemical features of either AML or acute lymphoblastic leukemia (ALL).] M0 AML appears to be associated with an inferior prognosis in non-Down syndrome patients. 8
• M1: acute myeloblastic leukemia with minimal differentiation but with the expression of MPO that is detected by immunohistochemistry or flow cytometry.
• M2: acute myeloblastic leukemia with differentiation.
• M3: acute promyelocytic leukemia (APL) hypergranular type.[Note: Identifying this subtype is critical since the risk of fatal hemorrhagic complication prior to or during induction is high and the appropriate therapy is different than for other subtypes of AML.] (Refer to the Acute Promyelocytic Leukemia section of this summary for more information on treatment options under clinical evaluation.)
• M3v: APL, microgranular variant. Cytoplasm of promyelocytes demonstrates a fine granularity, and nuclei are often folded. Same clinical, cytogenetic, and therapeutic implications as FAB M3.
• M4: acute myelomonocytic leukemia (AMML).
• M4Eo: AMML with eosinophilia (abnormal eosinophils with dysplastic basophilic granules).
• M5: acute monocytic leukemia (AMoL).
  • M5a: AMoL without differentiation (monoblastic).
  • M5b: AMoL with differentiation.

• M6: acute erythroid leukemia (AEL).
  • M6a: erythroleukemia.
  • M6b: pure erythroid leukemia.

• M7: acute megakaryocytic leukemia (AMKL). [Note: Diagnosis of M7 can be difficult without the use of flow cytometry as the blasts can be morphologically confused with lymphoblasts. Characteristically, the blasts display cytoplasmic blebs. Marrow aspiration can be difficult due to myelofibrosis, and marrow biopsy with reticulin stain can be helpful.]

Other extremely rare subtypes of AML include acute eosinophilic leukemia and acute basophilic leukemia.

Fifty percent to 60% of children with AML can be classified as having M1, M2, M3, M6, or M7 subtypes; approximately 40% have M4 or M5 subtypes. About 80% of children younger than 2 years with AML have an M4 or M5 subtype. The response to cytotoxic chemotherapy among children with the different subtypes of AML is relatively similar. One exception is FAB subtype M3, for which all-trans retinoic acid plus chemotherapy achieves remission and cure in approximately 70% to 80% of affected children.

World Health Organization (WHO) Classification System

In 2002, the WHO proposed a new classification system that incorporated diagnostic cytogenetic information and more reliably correlated with outcome. In this classification, patients with t(8;21), inv(16), t(15;17), and those with MLL translocations, which collectively constituted nearly half of the cases of childhood AML, were classified as AML with recurrent cytogenetic abnormalities. This classification system also decreased the bone marrow percentage of leukemic blast requirement for the diagnosis of AML from 30% to 20%; an additional clarification was made so that patients with recurrent cytogenetic abnormalities did not need to meet the minimum blast requirement to be considered AML. 9 10 11 In 2008, WHO expanded the number of cytogenetic abnormalities linked to AML classification, and for the first time included specific gene mutations (CEBPA and NPM mutations) in its classification system. 12 (Refer to the WHO classification of myeloid leukemias section of this summary for more information.) Such a genetically based classification system links AML class with outcome and provides significant biologic and prognostic information. With new emerging technologies aimed at genetic, epigenetic, proteomic, and immunophenotypic classification, AML classification will likely evolve and provide informative prognostic and biologic guidelines to clinicians and researchers.

WHO classification of AML
• AML with recurrent genetic abnormalities:
  • AML with t(8;21)(q22;q22), RUNX1-RUNX1T1 (CBFA/ETO).
  • AML with inv(16)(p13;q22) or t(16;16)(p13;q22), CBFB-MYH11.
  • APL with t(15;17)(q22;q11-12), PML-RARA.
  • AML with t(9;11)(p22;q23), MLLT3-MLL.
  • AML with t(6;9)(p23;q34), DEK-NUP214.
  • AML with inv(3)(q21;q26.2) or t(3;3)(q21;q26.2), RPN1-EVI1.
  • AML (megakaryoblastic) with t(1;22)(p13;q13), RBM15-MKL1.
  • AML with mutated NPM1.
  • AML with mutated CEBPA.

• AML with myelodysplasia-related features.
• Therapy-related myeloid neoplasms.
• AML, not otherwise specified:
  • AML with minimal differentiation.
  • AML without maturation.
  • AML with maturation.
  • Acute myelomonocytic leukemia.
  • Acute monoblastic and monocytic leukemia.
  • Acute erythroid leukemia.
  • Acute megakaryoblastic leukemia.
  • Acute basophilic leukemia.
  • Acute panmyelosis with myelofibrosis.

• Myeloid sarcoma.
• Myeloid proliferations related to Down syndrome:
  • Transient abnormal myelopoiesis.
  • Myeloid leukemia associated with Down syndrome.

• Blastic plasmacytoid dendritic cell neoplasm.

Histochemical Evaluation

The treatment for children with AML differs significantly from that for ALL. As a consequence, it is crucial to distinguish AML from ALL. Special histochemical stains performed on bone marrow specimens of children with acute leukemia can be helpful to confirm their diagnosis. The stains most commonly used include myeloperoxidase, periodic acid-Schiff (PAS), Sudan Black B, and esterase. In most cases the staining pattern with these histochemical stains will distinguish AML from AMML and ALL (see below). This approach is being replaced by immunophenotyping using flow cytometry.

Table 1. Histochemical Staining Patterns^a

^aRefer to the French-American-British (FAB) Classification for Childhood Acute Myeloid Leukemia section of this summary for more information about the morphologic-histochemical classification system for AML.^bThese reactions are inhibited by fluoride.

		M0	AML, APL (M1-M3)	AMML (M4)	AMoL (M5)	AEL (M6)	AMKL (M7)	ALL
Myeloperoxidase		-	+	+	-	-	-	-
Nonspecific esterases
	Chloracetate	-	+	+		-	-	-
	Alpha-naphthol acetate	-	-	+ b	+ b	-	b	-
Sudan Black B		-	+	+	-	-	-	-
PAS		-	-			+	-	+
AEL = acute erythroid leukemia; ALL = acute lymphoblastic leukemia; AML = acute myeloid leukemia; AMKL = acute megakaryocytic leukemia; AMML = acute myelomonocytic leukemia; AMoL = acute monocytic leukemia; APL = acute promyelocytic leukemia; PAS = periodic acid-Schiff.

Immunophenotypic Evaluation

The use of monoclonal antibodies to determine cell-surface antigens of AML cells is helpful to reinforce the histologic diagnosis. Various lineage-specific monoclonal antibodies that detect antigens on AML cells should be used at the time of initial diagnostic workup, along with a battery of lineage-specific T-lymphocyte and B-lymphocyte markers to help distinguish AML from ALL and bilineal (as defined above) or biphenotypic leukemias. The expression of various cluster determinant (CD) proteins that are relatively lineage-specific for AML include CD33, CD13, CD14, CDw41 (or platelet antiglycoprotein IIb/IIIa), CD15, CD11B, CD36, and antiglycophorin A. Lineage-associated B-lymphocytic antigens CD10, CD19, CD20, CD22, and CD24 may be present in 10% to 20% of AMLs, but monoclonal surface immunoglobulin and cytoplasmic immunoglobulin heavy chains are usually absent; similarly, CD2, CD3, CD5, and CD7 lineage-associated T-lymphocytic antigens are present in 20% to 40% of AMLs. 13 14 15 The aberrant expression of lymphoid-associated antigens by AML cells is relatively common but generally has no prognostic significance. 13 14

Immunophenotyping can also be helpful in distinguishing some FAB subtypes of AML. Testing for the presence of HLA-DR can be helpful in identifying APL. Overall, HLA-DR is expressed on 75% to 80% of AMLs but rarely expressed on APL. In addition, APL cases with PML/RARA were noted to express CD34/CD15 and demonstrate a heterogenous pattern of CD13 expression. 16 Testing for the presence of glycoprotein Ib, glycoprotein IIb/IIIa, or Factor VIII antigen expression is helpful in making the diagnosis of M7 (megakaryocytic leukemia). Glycophorin expression is helpful in making the diagnosis of M6 (erythroid leukemia). 17

Less than 5% of cases of acute leukemia in children are of ambiguous lineage, expressing features of both myeloid and lymphoid lineage. 18 19 20 These cases are distinct from ALL with myeloid coexpression in that the predominant lineage cannot be determined by immunophenotypic and histochemical studies. The definition of leukemia of ambiguous lineage varies among studies, although most investigators now use criteria established by the European Group for the Immunological Characterization of Leukemias (EGIL) or the more stringent WHO criteria. 21 22 23 In the WHO classification, the presence of MPO is required to establish myeloid lineage. This is not the case for the EGIL classification.

The WHO classification system is summarized in Table 2. 23 24

Table 2. Acute Leukemias of Ambiguous Lineage According to the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues^a

^aBéné MC: Biphenotypic, bilineal, ambiguous or mixed lineage: strange leukemias! Haematologica 94 (7): 891-3, 2009. Obtained from Haematologica/the Hematology Journal website http://www.haematologica.org.

Condition	Definition
Acute undifferentiated leukemia	Acute leukemia that does not express any marker considered specific for either lymphoid or myeloid lineage
Mixed phenotype acute leukemia with t(9;22)(q34;q11.2); BCR-ABL1	Acute leukemia meeting the diagnostic criteria for mixed phenotype acute leukemia in which the blasts also have the (9;22) translocation or the BCR-ABL1 rearrangement
Mixed phenotype acute leukemia with t(v;11q23); MLL rearranged	Acute leukemia meeting the diagnostic criteria for mixed phenotype acute leukemia in which the blasts also have a translocation involving the MLL gene
Mixed phenotype acute leukemia, B/myeloid, NOS	Acute leukemia meeting the diagnostic criteria for assignment to both B and myeloid lineage, in which the blasts lack genetic abnormalities involving BCR-ABL1 or MLL
Mixed phenotype acute leukemia, T/myeloid, NOS	Acute leukemia meeting the diagnostic criteria for assignment to both T and myeloid lineage, in which the blasts lack genetic abnormalities involving BCR-ABL1 or MLL
Mixed phenotype acute leukemia, B/myeloid, NOSrare types	Acute leukemia meeting the diagnostic criteria for assignment to both B- and T-lineage
Other ambiguous lineage leukemias	Natural killer cell lymphoblastic leukemia/lymphoma
NOS = not otherwise specified; WHO = World Health Organization.
24

Leukemias of mixed phenotype comprise two groups of patients: (1) bilineal leukemias in which there are two distinct population of cells, usually one lymphoid and one myeloid, and (2) biphenotypic leukemias where individual blast cells display features of both lymphoid and myeloid lineage. Biphenotypic cases represent the majority of mixed phenotype leukemias. 18 B-myeloid biphenotypic leukemias lacking the TEL-AML1 fusion have a lower rate of complete remission and a significantly worse event-free survival compared with patients with B-precursor ALL. 18 Some studies suggest that patients with biphenotypic leukemia may fare better with a lymphoid, as opposed to a myeloid, treatment regimen, 19 20 25 although the optimal treatment for patients remains unclear.

Cytogenetic Evaluation and Molecular Abnormalities

Chromosomal analyses of leukemia should be performed on children with AML because chromosomal abnormalities are important diagnostic and prognostic markers. 26 27 28 29 30 31 Clonal chromosomal abnormalities have been identified in the blasts of about 75% of children with AML and are useful in defining subtypes with particular characteristics (e.g., t(8;21) with M2, t(15;17) with M3, inv(16) with M4Eo, 11q23 abnormalities with M4 and M5, t(1;22) with M7). Leukemias with the chromosomal abnormalities t(8;21) and inv(16) are called core-binding factor leukemias; core-binding factor (a transcription factor involved in hematopoietic stem cell differentiation) is disrupted by each of these abnormalities.

Molecular probes and newer cytogenetic techniques (e.g., fluorescence in situ hybridization [FISH]) can detect cryptic abnormalities that were not evident by standard cytogenetic banding studies. 32 This is clinically important when optimal therapy differs, as in APL. Use of these techniques can identify cases of APL when the diagnosis is suspected but the t(15;17) is not identified by routine cytogenetic evaluation. The presence of the Philadelphia (Ph) chromosome in patients with AML most likely represents chronic myelogenous leukemia (CML) that has transformed to AML rather than de novo AML. Molecular methods are also being used to identify recurring gene mutations in adults and children with AML, and as described below, some of these recurring mutations have prognostic significance.

A unifying concept for the role of specific mutations in AML is that mutations that promote proliferation (Type I) and mutations that block normal myeloid development (Type II) are required for full conversion of hematopoietic stem/precursor cells to malignancy. 33 34 Support for this conceptual construct comes from the observation that there is generally mutual exclusivity within each type of mutation, such that a single Type I and a single Type II mutation are present within each case. Further support comes from genetically engineered models of AML for which cooperative events rather than single mutations are required for leukemia development. Type I mutations are commonly in genes involved in growth factor signal transduction and include mutations in FLT3, KIT, NRAS, KRAS, and PTNP11. 35 Type II genomic alterations include the common translocations and mutations associated with favorable prognosis (t(8;21), inv(16), t(16;16), t(15;17), CEBPA, and NPM1). MLL rearrangements (translocations and partial tandem duplication) are also classified as Type II mutations.

Specific recurring cytogenetic and molecular abnormalities are briefly described below. The abnormalities are listed by those in clinical use that identify patients with favorable or unfavorable prognosis, followed by other abnormalities.

Molecular abnormalities associated with favorable prognosis include the following:
• t(8;21): In leukemias with t(8;21), the AML1 (RUNX1) gene on chromosome 21 is fused with the ETO (RUNX1T1) gene on chromosome 8. The t(8;21) translocation is associated with the FAB M2 subtype and with granulocytic sarcomas. 36 37 Adults with t(8;21) have a more favorable prognosis than adults with other types of AML. 26 38 These children have a more favorable outcome compared with children with AML characterized by normal or complex karyotypes 26 39 40 41 with 5-year overall survival (OS) of 80% to 90%. 29 30
• inv(16): In leukemias with inv(16), the CBF beta gene at chromosome band 16q22 is fused with the MYH11 gene at chromosome band 16p13. The inv(16) translocation is associated with the FAB M4Eo subtype. 42 Inv(16) confers a favorable prognosis for both adults and children with AML 26 39 40 41 with a 5-year OS of about 85%. 29 30 Inv(16) occurs in 7% to 9% of children with AML. 29 30
• t(15;17): AML with t(15;17) is invariably associated with APL, a distinct subtype of AML that is treated differently than other types of AML because of its marked sensitivity to the differentiating effects of all-trans retinoic acid. The t(15;17) translocation leads to the production of a fusion protein involving the retinoid acid receptor alpha and PML. 43 Other much less common translocations involving the retinoic acid receptor alpha can also result in APL (e.g., t(11;17) involving the PLZF gene). 44 Identification of cases with the t(11;17) is important because of their decreased sensitivity to all-trans retinoic acid. 43 44 APL represents about 7% of children with AML. 30 45
• Nucleophosmin (NPM1) mutations: NPM1 is a protein that has been linked to ribosomal protein assembly and transport as well as being a molecular chaperone involved in preventing protein aggregation in the nucleolus. Immunohistochemical methods can be used to accurately identify patients with NPM1 mutations by the demonstration of cytoplasmic localization of NPM. 46 Mutations in the NPM1 protein that diminish its nuclear localization are primarily associated with a subset of AML with a normal karyotype, absence of CD34 expression, 47 and an improved prognosis in the absence of FLT3-internal tandem duplication (ITD) mutations in adults and younger adults. 47 48 49 50 51 52

  Studies of children with AML suggest a lower rate of occurrence of NPM1 mutations in children compared with adults with normal cytogenetics. mutations in children compared with adults with normal cytogenetics. NPM1 mutations occur in approximately 8% of pediatric patients with AML and are uncommon in children younger than 2 years. mutations occur in approximately 8% of pediatric patients with AML and are uncommon in children younger than 2 years. 34 53 54 55 NPM1 mutations are associated with a favorable prognosis in patients with AML characterized by a normal karyotype. mutations are associated with a favorable prognosis in patients with AML characterized by a normal karyotype. 34 54 55 For the pediatric population, conflicting reports have been published regarding the prognostic significance of a For the pediatric population, conflicting reports have been published regarding the prognostic significance of a NPM1 mutation when a mutation when a FLT3-ITD mutation is also present, with one study reporting that a -ITD mutation is also present, with one study reporting that a NPM1 mutation did not completely abrogate the poor prognosis associated with having a mutation did not completely abrogate the poor prognosis associated with having a FLT3-ITD mutation,-ITD mutation, 54 56 but with other studies showing no impact of a but with other studies showing no impact of a FLT3-ITD mutation on the favorable prognosis associated with a -ITD mutation on the favorable prognosis associated with a NPM1 mutation. mutation. 34 55

• CEBPA mutations: Mutations in the CCAAT/Enhancer Binding Protein Alpha gene (CEBPA) occur in a subset of children and adults with cytogenetically normal AML. In adults younger than 60 years, approximately 15% of cytogenetically normal AML cases have mutations in CEBPA. 51 57 Outcome for adults with AML with CEBPA mutations appears to be relatively favorable and similar to that of patients with core-binding factor leukemias. 51 57 Studies in adults with AML have demonstrated that CEBPA double-mutant, but not single-allele mutant, AML was independently associated with a favorable prognosis. 58 59 60

  CEBPA mutations occur in 5% to 8% of children with AML and have been preferentially found in the cytogenetically normal subtype of AML with FAB M1 or M2; 70% to 80% of pediatric patients have double-mutant alleles, which is predictive of a significantly improved survival and similar to the effect observed in adult studies. mutations occur in 5% to 8% of children with AML and have been preferentially found in the cytogenetically normal subtype of AML with FAB M1 or M2; 70% to 80% of pediatric patients have double-mutant alleles, which is predictive of a significantly improved survival and similar to the effect observed in adult studies. 61 62 Although both double- and single-mutant alleles of Although both double- and single-mutant alleles of CEBPA were associated with a favorable prognosis in children with AML in one large study, were associated with a favorable prognosis in children with AML in one large study, 61 a second study observed inferior outcome for patients with single a second study observed inferior outcome for patients with single CEBPA mutations. mutations. 62 However, very low numbers of children with single-allele mutants were included in these two studies (only 13 However, very low numbers of children with single-allele mutants were included in these two studies (only 13 in toto), making a conclusion regarding the prognostic significance of single-allele ), making a conclusion regarding the prognostic significance of single-allele CEBPA mutations in children premature. mutations in children premature. 61

Molecular abnormalities associated with an unfavorable prognosis include the following:
• Chromosomes 5 and 7: Chromosomal abnormalities associated with poor prognosis in adults with AML include those involving chromosome 5 (monosomy 5 and del(5q)) and chromosome 7 (monosomy 7). 26 38 These cytogenetic subgroups represent approximately 2% and 4% of pediatric AML cases, respectively, and are also associated with poor prognosis in children. 29 38 63 64 65 In the past, patients with del(7q) were also considered to be at high risk of treatment failure and data from adults with AML support a poor prognosis for both del(7q) and monosomy 7. 31 However, outcome for children with del(7q), but not monosomy 7, appears to be comparable to that of other children with AML. 30 65 The presence of del(7q) does not abrogate the prognostic significance of favorable cytogenetic characteristics (e.g., inv(16) and t(8;21)). 26 65 66
• Chromosome 3 (inv(3)(q21;q26) or t(3;3)(q21;q26)) and EVI1 overexpression: The inv(3) and t(3;3) abnormalities involving the EVI1 gene located at chromosome 3q26 are associated with poor prognosis in adults with AML, 26 38 67 but are very uncommon in children (<1% of pediatric AML cases). 29 40 68
• FLT3 mutations: Presence of a FLT3-ITD mutation appears to be associated with poor prognosis in adults with AML, 69 particularly when both alleles are mutated or there is a high ratio of the mutant allele to the normal allele. 70 71 FLT3-ITD mutations also convey a poor prognosis in children with AML. 56 72 73 74 75 76 The frequency of FLT3-ITD mutations in children is lower than that observed in adults, especially for children younger than 10 years, for whom 5% to 10% of cases have the mutation (compared with approximately 30% for adults). 74 75 77 A longer length of the ITD segment of FLT3-ITD has been reported to be associated with a poorer outcome. 78

  Presence of the FLT3-ITD mutation is strongly associated with the microgranular variant (M3v) of APL and with hyperleukocytosis.-ITD mutation is strongly associated with the microgranular variant (M3v) of APL and with hyperleukocytosis. 73 79 80 It remains unclear whether It remains unclear whether FLT3 mutations are associated with poorer prognosis in patients with APL who are treated with modern mutations are associated with poorer prognosis in patients with APL who are treated with modern therapy that includes all-trans retinoic acid.therapy that includes all-trans retinoic acid. 80 81 82 83

  Activating point mutations of FLT3 have also been identified in both adults and children with AML, have also been identified in both adults and children with AML, 70 74 84 though the clinical significance of these mutations is not clearly defined. though the clinical significance of these mutations is not clearly defined. FLT3-ITD and point mutations occur in 30% to 40% of children and adults with APL.-ITD and point mutations occur in 30% to 40% of children and adults with APL. 73 79 81 82 The prognostic significance of this mutation in APL is unclear, although a mutant to wild type allelic ratio of greater than or equal to 0.5 may be associated with a worse outcome. The prognostic significance of this mutation in APL is unclear, although a mutant to wild type allelic ratio of greater than or equal to 0.5 may be associated with a worse outcome. 85

Other molecular abnormalities observed in pediatric AML include the following:
• MLL gene rearrangements: Translocations of chromosomal band 11q23 involving the MLL gene, including most AML secondary to epipodophyllotoxin, 86 are associated with monocytic differentiation (FAB M4 and M5). The most common translocation, representing approximately 50% of MLL-rearranged cases in the pediatric AML population, is t(9;11)(p22;q23) in which the MLL gene is fused with the AF9 gene. 87 However, more than 50 different fusion partners have been identified for the MLL gene in patients with AML. The median age for 11q23/MLL-rearranged cases in the pediatric AML setting is approximately 2 years and most translocation subgroups have a median age at presentation of younger than 5 years. 87 However, pediatric cases with t(6;11)(q27;q23) and t(11;17)(q23;q21) have significantly older median ages at presentation (12 years and 9 years, respectively). 87

  Outcome for patients with de novo AML and AML and MLL gene rearrangement are generally reported as being similar to that for other patients with AML. gene rearrangement are generally reported as being similar to that for other patients with AML. 26 87 88 However, as the However, as the MLL gene can participate in translocations with many different fusion partners, the specific fusion partner appears to influence prognosis as demonstrated by a large international retrospective study evaluating outcome for 756 children with 11q23- or gene can participate in translocations with many different fusion partners, the specific fusion partner appears to influence prognosis as demonstrated by a large international retrospective study evaluating outcome for 756 children with 11q23- or MLL-rearranged AML.-rearranged AML. 87 For example, cases with t(1;11)(q21;q23), representing 3% of all 11q23/ For example, cases with t(1;11)(q21;q23), representing 3% of all 11q23/MLL-rearranged AML, showed a highly favorable outcome with 5-year event-free survival (EFS) of 92%. While several reports have described more favorable prognosis for cases with t(9;11), in which the -rearranged AML, showed a highly favorable outcome with 5-year event-free survival (EFS) of 92%. While several reports have described more favorable prognosis for cases with t(9;11), in which the MLL gene is fused with the gene is fused with the AF9 gene, the international retrospective study did not confirm the favorable prognosis of the t(9;11)(p22;q23) subgroup. gene, the international retrospective study did not confirm the favorable prognosis of the t(9;11)(p22;q23) subgroup. 26 87 89 90 91 A similarly inferior outcome for patients with t(9;11) AML was reported from the AML-BFM 98 study. A similarly inferior outcome for patients with t(9;11) AML was reported from the AML-BFM 98 study. 30 A follow-up study demonstrated that additional cytogenetic abnormalities further influenced outcome, with complex karyotypes and trisomy 19 predicting poor outcome and trisomy 8 predicting a more favorable outcome. A follow-up study demonstrated that additional cytogenetic abnormalities further influenced outcome, with complex karyotypes and trisomy 19 predicting poor outcome and trisomy 8 predicting a more favorable outcome. 92

  Several 11q23/MLL-rearranged AML subgroups are associated with poor outcome. For example, cases with the t(10;11) translocation are a group at particularly high risk of relapse in bone marrow and the central nervous system (CNS).-rearranged AML subgroups are associated with poor outcome. For example, cases with the t(10;11) translocation are a group at particularly high risk of relapse in bone marrow and the central nervous system (CNS). 26 30 93 Some cases with the t(10;11) translocation have fusion of the Some cases with the t(10;11) translocation have fusion of the MLL gene with the gene with the AF10//MLLT10 at 10p12, while others have fusion of at 10p12, while others have fusion of MLL with with ABI1 at 10p11.2. at 10p11.2. 94 95 The international retrospective study found that these cases, which present at a median age of approximately 1 year, have a 5-year EFS in the 20% to 30% range. The international retrospective study found that these cases, which present at a median age of approximately 1 year, have a 5-year EFS in the 20% to 30% range. 87 Patients with t(6;11)(q27;q23) and with t(4;11)(q21;q23) also show poor outcome, with a 5-year EFS of 11% and 29%, respectively. Patients with t(6;11)(q27;q23) and with t(4;11)(q21;q23) also show poor outcome, with a 5-year EFS of 11% and 29%, respectively. 87 An international collaborative study of 733 children with de novo 11q23/ An international collaborative study of 733 children with de novo 11q23/MLL-rearranged AML showed prognostic significance after multivariate analysis with: (1) specific translocation partners (10p12, hazard ratio for EFS 1.36, OS 1.62, relapse 1.76; 6q27, EFS 2.29, OS 2.72, relapse 2.79; 1q21, EFS 0.12; 10p11.2, EFS 2.12, OS 2.56); (2) selected trisomies (trisomy 8, EFS 0.57, OS 0.54; trisomy 19, EFS 1.77, OS 2.11); and (3) additional structural chromosomal aberrations (EFS 1.39).-rearranged AML showed prognostic significance after multivariate analysis with: (1) specific translocation partners (10p12, hazard ratio for EFS 1.36, OS 1.62, relapse 1.76; 6q27, EFS 2.29, OS 2.72, relapse 2.79; 1q21, EFS 0.12; 10p11.2, EFS 2.12, OS 2.56); (2) selected trisomies (trisomy 8, EFS 0.57, OS 0.54; trisomy 19, EFS 1.77, OS 2.11); and (3) additional structural chromosomal aberrations (EFS 1.39). 92

• t(6;9): t(6;9) leads to the formation of a leukemia-associated fusion protein DEK-NUP214. 96 This subgroup of AML has been associated with a poor prognosis in adults with AML, 96 97 98 and occurs infrequently in children (approximately 2% of AML cases). This subtype appears to be associated with a high risk of treatment failure in children. 29
• t(1;22): The t(1;22)(p13;q13) translocation is uncommon (<1% of pediatric AML) and is restricted to acute megakaryocytic leukemia (AMKL). 29 99 100 101 Most AMKL cases with t(1;22) occur in infants, and the translocation is uncommon in children with Down syndrome who develop AMKL. 99 101 In leukemias with t(1;22), the OTT (RBM15) gene on chromosome 1 is fused to the MAL (MLK1) gene on chromosome 22. 102 103 Cases with detectable OTT/MAL fusion transcripts in the absence of t(1;22) have been reported, as well. 101 In the small number of children reported, the presence of the t(1;22) appears to be associated with poor prognosis, though long-term survivors have been noted following intensive therapy. 101 104
• 12p: Cytogenetically detectable aberrations on the short arm of chromosome 12 are uncommon in unselected pediatric AML patients (2%4%) and appear to predict poor outcome. 29 30

  A subset of patients with 12p abnormalities have the t(7;12)(q36;p13) translocation involving ETV6 on chromosome 12p13 and on chromosome 12p13 and HLXB9 on chromosome 7q36. on chromosome 7q36. 105 This alteration occurs virtually exclusively in children younger than 2 years, is mutually exclusive with This alteration occurs virtually exclusively in children younger than 2 years, is mutually exclusive with MLL rearrangement, and is associated with a high risk of treatment failure. rearrangement, and is associated with a high risk of treatment failure. 29 30 34 106 107

• NUP98/NSD1 translocation: The NUP98/NSD1 translocation, which is often cytogenetically cryptic, results in the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35). 108 109 110 111 112 This alteration occurs in approximately 4% of pediatric AML cases. 110 112 NUP98/NSD1 cases have not been observed in children younger than 2 years, 108 109 110 111 112 and they present with high WBC (median 147 í 10⁹/L in one study). 112 Most NUP98/NSD1 AML cases do not show cytogenetic aberrations, 108 112 although del(5q) is noted in some. 110 111 A high percentage of NUP98/NSD1 cases (91% in one study) have FLT3-ITD. 112 Presence of NUP98/NSD1 independently predicted for poor prognosis, and children with NUP98/NSD1 AML had a high risk of relapse with a resulting 4-year EFS of approximately 10%. 112
• RAS mutations: Although mutations in RAS have been identified in 20% to 25% of patients with AML, the prognos