IntroductionChildhood acute myeloid leukemia (AML) is a rare and heterogeneous disease, with an incidence of 7 cases per million children younger than 15 years. In high-income countries, intensive therapy in conjunction with effective supportive care has increased survival rates to ϳ 70%. In 1990 and 2003, expert working groups made recommendations for diagnosis, outcomes, standardization of response criteria, and reporting standards for AML. 1,2 Recent improvements in identifying the molecular genetics and pathogenesis of AML have been implemented in the new World Health Organization (WHO) classification of AML. 3 These changes, and the definition of new diagnostic and prognostic markers and their associated targeted therapies, have prompted the update of earlier recommendations by an international group, on behalf of the European LeukemiaNet for AML in adults in 2010. 4 Despite broad overlap in the diagnostic and treatment recommendations for AML for children and adults, there are important differences in both the diagnostic criteria and disease management, which merit age-specific recommendations. The absence of published recommendations specific for pediatric AML motivated an international group of pediatric hematologists and oncologists (panel and participating groups see "Appendix") to develop evidence-and expert opinionbased consensus recommendations for the diagnosis and management of AML in children, incorporating emerging information on the biology of the disease. The scope of the review is presented in the "Appendix." Recommendations for specific subgroups are also included. This article discusses diagnostic procedures and initial workup, prognostic factors, response criteria, and management, and in particular focuses on differences between adults and children with AML. For personal use only. on May 12, 2018. by guest www.bloodjournal.org From WHO classification and pediatric AMLThe recent WHO 2008 classification is applicable to both adult and pediatric AML 3,5 and has been summarized by Döhner et al. 4 The classification contains most, but not all, cytogenetic subgroups specific to children. Differences in genetic background between children and adults are given in Table 1 and discussed further in "Cytogenetics."Compared with previous classifications (European Group of Immunologic Characterization of Leukemias [EGIL], WHO 2001), 6 the new WHO classification introduced a stringently defined subclass of acute leukemias of ambiguous lineage (mixed phenotype acute leukemias [MPALs]), mainly on the basis of detailed immunophenotypic criteria (Table 2) or presence of t(9;22)(q34; q11.2)/BCR-ABL1 or t(v;11q23)/MLL rearrangement. 3,5,6 The new classification aims to create uniform subgroups defined by unifying molecular targets, which allow selection of specific treatment. Diagnostic procedures and initial workupThe minimal diagnostic requirements in childhood AML are morphology with cytochemistry, immunophenotyping, karyotyping, FISH, and specific molecular genetics in the bone marrow, which is comparable ...

Four thousand, four hundred and forty eligible children of up to 18 years of age were treated in four consecutive trials between 1981 and 1995 with the treatment protocols of the Berlin-Frankfurt-Münster (BFM) study group for childhood acute lymphoblastic leukemia (ALL). The probability for event-free survival (pEFS) at 8 years improved from 65.8% in study ALL-BFM 81 to 75.9% in study ALL-BFM 90. The cumulative incidence of recurrences with CNS involvement was 10.1% and 9.3% in studies ALL-BFM 81 and 83, but was reduced to less than 5% in study ALL-BFM 90 (for isolated CNS relapses from 5.3% in study ALL-BFM 81 to 1.1% in study ALL-BFM 90). Four major findings were derived from this series of trials performed by 37 to 96 centers in Germany, Austria, and Switzerland: (1) Reintensification is a crucial part of treatment, even in low risk patients; (2) presymptomatic cranial radiotherapy can be safely reduced to 12 Gy, or even be eliminated if it is replaced by early intensive systemic and intrathecal methotrexate applied; (3) maintenance therapy given a total of 24 months from diagnosis provides a lower rate of systemic relapses than treatment for 18 months; (4) inadequate response to an initial 7-day prednisone window (combined with one intrathecal injection of methotrexate on day 1) defines about 10% of the patients with a very high risk of relapse. For patients with adequate early response (90% of all) an 8-year pEFS of 80% has been achieved in the most recent trial ALL-BFM 90. While it has proven so far to be impossible to improve the outcome for the small group of high risk patients, the number of recurrences could be effectively reduced for the large group of patients responding adequately to the prednisone in vivo sensitivity test. Apart from inadequate prednisone response, patients with hyperleukocytosis, age <1 year, or the presence of the Philadelphia-chromosome (Ph+ ALL) are at a particularly high risk of failure.

Translocations involving chromosome 11q23 frequently occur in pediatric acute myeloid leukemia (AML) and are associated with poor prognosis. In most cases, the MLL gene is involved, and more than 50 translocation partners have been described. Clinical outcome data of the 11q23-rearranged subgroups are scarce because most 11q23 series are too small for meaningful analysis of subgroups, although some studies suggest that patients with t(9;11)(p22;q23) have a more favorable prognosis. We retrospectively collected outcome data of 756 children with 11q23-or MLL-rearranged AML from 11 collaborative groups to identify differences in outcome based on translocation partners. All karyotypes were centrally reviewed before assigning patients to subgroups. The event-free survival of 11q23/ MLL-rearranged pediatric AML at 5 years from diagnosis was 44% (؎ 5%), with large differences across subgroups (11% ؎ 5% to 92% ؎ 5%). Multivariate analysis identified the following subgroups as independent prognostic predictors: t(1;11)(q21;q23) (hazard ratio [HR] ‫؍‬ 0.1, P ‫؍‬ .004); t(6; 11)(q27;q23) (HR ‫؍‬ 2.2, P < .001); t(10; 11)(p12;q23) (HR ‫؍‬ 1.5, P ‫؍‬ .005); and t(10;11)(p11.2;q23) (HR ‫؍‬ 2.5, P ‫؍‬ .005). We could not confirm the favorable prognosis of the t(9;11)(p22;q23) subgroup. We identified large differences in outcome within 11q23/MLL-rearranged pediatric AML and novel subgroups based on translocation partners that independently predict clinical outcome. Screening for these translocation partners is needed for accurate treatment stratification at diagnosis. (Blood. 2009;114:2489-2496)

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Chromosomal rearrangements of the human MLL gene are associated with high-risk pediatric, adult and therapy-associated acute leukemias. These patients need to be identified, treated appropriately and minimal residual disease was monitored by quantitative PCR techniques. Genomic DNA was isolated from individual acute leukemia patients to identify and characterize chromosomal rearrangements involving the human MLL gene. A total of 760 MLL-rearranged biopsy samples obtained from 384 pediatric and 376 adult leukemia patients were characterized at the molecular level. The distribution of MLL breakpoints for clinical subtypes (acute lymphoblastic leukemia, acute myeloid leukemia, pediatric and adult) and fused translocation partner genes (TPGs) will be presented, including novel MLL fusion genes. Combined data of our study and recently published data revealed 104 different MLL rearrangements of which 64 TPGs are now characterized on the molecular level. Nine TPGs seem to be predominantly involved in genetic recombinations of MLL: AFF1/AF4, MLLT3/ AF9, MLLT1/ENL, MLLT10/AF10, MLLT4/AF6, ELL, EPS15/AF1P, MLLT6/AF17 and SEPT6, respectively. Moreover, we describe for the first time the genetic network of reciprocal MLL gene fusions deriving from complex rearrangements.

The trial ALL-BFM 95 for treatment of childhood acute lymphoblastic leukemia was designed to reduce acute and longterm toxicity in selected patient groups with favorable prognosis and to improve outcome in poor-risk groups by treatment intensification. These aims were pursued through a stratification strategy using white blood cell count, age, immunophenotype, treatment response, and unfavorable genetic aberrations providing an excellent discrimination of risk groups.

Summary We examined the leukemic stem cell potential of blasts at different stages of maturation in childhood acute lymphoblastic leukemia. Human leukemic bone marrow was transplanted intrafemorally into NOD/scid mice. Cells sorted using the B precursor differentiation markers CD19, CD20 and CD34 were isolated from patient samples and engrafted mice before serial transplantation into primary or subsequent (up to quaternary) recipients. Surprisingly, blasts representative of all the different maturational stages were able to reconstitute and re-establish the complete leukemic phenotype in vivo. Sorted blast populations mirrored normal B precursor cells with transcription of a number of stage-appropriate genes. These observations have informed a model for leukemia-propagating stem cells in childhood ALL.

High-level expression of the cytokine receptor-like factor 2 gene, CRLF2, in precursor B-cell acute lymphoblastic leukemia (pB-ALL) was shown to be caused by a translocation involving the IGH@ locus or a deletion juxtaposing CRLF2 with the P2RY8 promoter. To assess its possible prognostic value, CRLF2 expression was analyzed in 555 childhood pB-ALL patients treated according to the Acute Lymphoblastic Leukemia Berlin-Frankfurt-Münster 2000 (ALL-BFM 2000) protocol. Besides CRLF2 rearrangements, high-level CRLF2 expression was seen in cases with supernumerary copies of the CRLF2 locus. On the basis of the detection of CRLF2 rearrangements, a CRLF2 high-expression group (n = 49) was defined. This group had a 6-year relapse incidence of 31% plus or minus 8% compared with 11% plus or minus 1% in the CRLF2 low-expression group (P = .006). This difference was mainly attributable to an extremely high incidence of relapse (71% ± 19%) in non–high-risk patients with P2RY8-CRLF2 rearrangement. The assessment of CRLF2 aberrations may therefore serve as new stratification tool in Berlin-Frankfurt-Münster–based protocols by identifying additional high-risk patients who may benefit from an intensified and/or targeted treatment.