**Genomics of Acute Myeloid Leukemia**

**Genomics of Acute Myeloid Leukemia**

Zeeshan Ansar Ahmed, Imran Ahmed Siddqui and Sadia Sultan Sadia Sultan Additional information is available at the end of the chapter

Zeeshan Ansar Ahmed, Imran Ahmed Siddqui and

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72757

#### **Abstract**

Acute myelogenous leukemia (AML) is a clonal, malignant disease of hematopoietic tissue that is characterized by accumulation of abnormal (leukemic) blast cells, principally in the bone marrow. Representation of these genetic mutations and the involvement patterns seems to follow specific and temporally ordered fluctuating manners. Somatic mutations in these genes are represented as a variety of recurrent chromosomal abnormalities, e.g., t (8;21), t(15;17), etc., or by the presence of prognostic markers, e.g., FLT3, MLL, NPM1 and CEBPA as well as encoding epigenetic modifiers, such as DNMT3A, ASXL1, TET2, IDH1, and IDH2, are commonly acquired early and are present in the founding clone. The same genes are frequently found to be mutated in elderly individuals along with clonal expansion of hematopoiesis that confers an increased risk for the development of hematologic cancers. Furthermore, such genomic changes may persist after therapy, lead to clonal expansion during hematologic remission, and eventually lead to relapsed disease. Majority of genetic data are now being used to classification, risk stratification, and clinical care of patients. The unprecedented molecular characterization provided by advanced and deeply sensitized molecular assays like next-generation sequencing (NGS) offers the potential for an individualized approach to treatment in AML, bringing us one step closer to personalized medicine.

DOI: 10.5772/intechopen.72757

**Keywords:** acute myeloid leukemia, mutation, Fms-like tyrosine kinase 3 receptor, next-generation sequencing, targeted AML therapy

#### **1. Introduction**

The acute myeloid leukemia (AML) is a malignant tumor of hematopoietic precursor cells of non-lymphoid lineage, arising in the bone marrow. It is diagnosed on the basis of clinical features, peripheral and bone marrow morphology, cytochemical stains, immunophenotyping, and cytogenetic analysis [1].

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Novel molecular markers of prognostic and more importantly of predictive significance have been identified in different leukemias. The link between the leukemogenic importance of these markers and their role as potential targets for novel drugs has started to contribute to the stepwise replacement of risk adapted by treatment strategies, e.g., imatinib in chronic myeloid leukemia (CML) and all-trans-retinoic acid (ATRA) in acute promyelocytic leukemia (APL).

initiate leukemic phase. Chromosomal derangement leads to disruption of transcription factor that controls directly hematopoiesis. Example is RARα that is formed by realignment of 17q21 [12]. Besides fusion genes other chromosomal abnormalities are also important in pathogenesis of AML. These are divided into three groups. (1) mutations abnormally controlled transcription factors that are helpful in hematopoieses, (2) mutations related to certain receptors, i.e., tyrosine kinase receptors, and (3) mutations involving the gene that encodes nucleophosmin [13].

Genomics of Acute Myeloid Leukemia http://dx.doi.org/10.5772/intechopen.72757 67

Hematopoiesis is regulated by various transcriptions factors which encodes with genes. These genes can get mutation which leads to inactivated or dominated in regulation of hematopoietic functions. Indeed, AML1mutations are detected in up to 25% of M0 cases and are frequently biallelic [14]. The CEBPA, which plays an important role in granulopoiesis, also is a relatively common target in AML, being potentially deregulated by the AML1-ETO and promyelocytic leukemia-retinoic acid receptor alpha (PML-RARα) oncoproteins. Furthermore,

Evaluation of karyotypic abnormalities has prognostic and therapeutic implications. Detection of t(15:17) by cytogenetic analysis shows favorable treatment response by ATRA. Similarly, t(9:22) is not responded to conventional chemotherapy but showed good results to imatinib. Approximately 60% of newly diagnosed cases with less than 20% blasts in the bone marrow have abnormal karyotype. Prognostically, t(15:17),inv(16), and t(8:21) showed relatively bet-

The absence of fusion genes in good prognostic group necessitates evaluation by FISH to accurately define prognosis. This can be exemplified by complex pattern of losses and loss of chromosome 5 or 7. Other than FISH, southern blot analysis can be used for chromosomal abnormality evaluation. However, it is more laborious than real-time PCR but more informative in certain circumstances, i.e., MLL gene rearrangement [17]. This approach can be used in

The most notable is FLT3-ITD, which is associated with decreased duration of remission. However, its impact on survival after post bone marrow transplant in the first CR is not clearly documented [18]. The presence of EVI1 in the absence of chromosome 3q abnormalities depicts poor survival. Mutations that show good response to conventional chemotherapy and do not need bone marrow transplant in the first CR are the presence of NPM1 or CEBPA mutation without concomitant FLT3-ITD mutation [19]. In the era of molecular medicine, new tests at molecular levels are being under process. New molecularly targeted agents are underway on the basis of these special tests. Examples of these are FLT3 inhibitors that can modify

mutations involving CEBPA are present in approximately 10% of cases of AML [15].

**2.2. Abrasions in gene associated with transcription**

ter prognosis in comparison to monosomies 5 or 7 [16].

the future for minimal residual disease assessment in AML.

**2.4. Chromosomal aberration detection by FISH**

**2.5. Predictive mutations in leukemogenesis**

outcome of poor prognostic group.

**2.3. Karyotypic abnormalities in AML**

Over the past few decades, it has become clear that a significant proportion of cases of AML are characterized by at least one of a varieties of recurrent chromosomal abnormalities, e.g., t (8;21), t(15;17), etc., or by the presence of prognostic markers, e.g., FMS-like tyrosine kinase 3 (FLT3), multilineage leukemia (MLL), nucleophosmin 1 (NPM1) and CCAAT/enhancerbinding protein-α (CEBPA). A key challenge for the future is to use information gained from cytogenetic analysis in conjunction with molecular diagnosis and gene expression profiling to achieve greater consensus in the risk group assignment of AML, and risk adapted therapy.

FLT 3 is widely known as FLT3 is a class III tyrosine kinase receptor [2]. Its structure consists of an extracellular ligand-binding domain, a single transmembrane domain, and a cytoplasmic region consisting of juxtamembrane domain and kinase domain interrupted by kinase insert [2, 3]. FLT3 is normally expressed on hematopoietic progenitor stem cells (HPSCs) where it plays an important role in survival and proliferation of stem cells. Its expression is lost with HPSC differentiation [2].

FLT3 mutations have been detected in one-third of AML patients and a small number of ALL patients [2].The mutations most commonly involve internal tandem duplications (ITDs) of the juxtamembrane domain (JM) (detected in 23% of AML patients and <1% of ALL patients) and point mutations in the activation loop of tyrosine kinase domain [2–4]. It has been detected in 7–12% of AML patients and about 3% of ALL patients [4, 5].

Prevalence of FLT3-ITD is according to age, i.e., rare in infants. FLT3 positivity was reported to be 5–10% in patients younger than 10 years, but it rose to 35% in middle-aged patients. Patients with this mutation usually present with increased white blood counts (WBC) and have normal cytogenetics [6]. In literature, there is no marked difference in complete response (CR) between FLT3 positive and FLT 3 negative patients, but relapse rate and overall survival(OS) are lower in FLT3-ITD-positive patients specially in younger than 60 years [7].

Further studies have confirmed that FLT3-ITD is not only inversely correlated with relapse but also associated with decreased overall survival [8–10]. In Kottaridis study, the prevalence of FLT3ITD was 27%. In same study, this mutation was strongly associated with hyperleukocytosis and normal cytogenetics. In literature, on multivariate analysis this mutation has the strongest correlation with decrease DFS [10].
