**1. Introduction**

#### **1.1 Acute myeloid leukemia (AML)**

Acute myeloid leukemia (AML) is a heterogeneous malignant disease of the hematopoietic system, marked by mutational arrest of myeloid lineage precursor cells and limited myeloid differentiation capacity [1]. Theoretically, malignant transformation can arise at any level at which cell precursors are capable of selfrenewal. However, the hematopoietic precursors are typically arrested in the earliest stages of myeloid maturation pathway - myeloblasts or promyelocytes. The malignant cells suppress the normal hematopoiesis by accumulating in the bone marrow and displacing the normal hematopoietic stem cells, resulting in depletion of normal blood cells. Тhe presence of more than 20% myeloblasts in the bone marrow or peripheral blood, as assessed by morphological evaluation of blood smears and bone marrow aspirate smears is diagnostic for AML. Morphologically, AML cells resemble normal myeloblasts to some extent, although they are distinguished by specific features, such as Auer Bodies – crystalloid azurophylic granules or Auer Rods – needle-shaped conglomerates of granules. Immunophenotyping, cytogenetics and molecular genetics must be employed to confirm the diagnosis of AML and further characterize the AML subtype [1].

AML is one of the most common types of leukemia in adults, as stated by American Society of Cancer, the second most common, following chronic lymphocytic leukemia (CLL), but the leading cause of mortality of leukemic deaths [2]. The median age at diagnosis is approximately 70 years. The estimated annual age-standardized incidence rate is 4.3 per 100.000, more precisely, from 1.3 per 100.000 in patients younger than 65 years and 12.2 per 100.000 in patients older than 65 [2, 3].

The etiology of de novo cases of AML is quite obscure. Only a small portion of all AML cases - around 10%, are secondary AML, due to transformation of prior hematological malignancy, such as myelodisplastic syndrome (MDS) or myeloproliferative neoplasm (MPN). Around another 10% of all cases arise from suggested DNA damage of known previous factor, as prior therapy with alkylating agents or topoisomerases, or prior radiotherapy [4].

#### **1.2 WHO classification of AML**

The revised fourth revision to the World Health Organization classification of Tumors of Hematopoietic and Lymphoid Tissues, published in 2017, distinguishes six AML subtypes and it incorporates cytogenetic and molecular abnormalities into diagnostic algorithms, in contrast to previous classifications of AML, based on morphology and immunophenotype [5]. The entity "AML with recurrent genetic abnormalities" comprises 11 subcategories of AML, with acute promyelocitic leukemia (APL with PML-RARA) included. The abnormalities that are not included in this group are considered to be rare among adult population. Six well-defined recurrent balanced translocations and inversions and their variants are covered within this classification. Two entities included are new provisional subcategories: AML with *BCR-ABL1* fusion gene and AML with mutated *RUNX1*. Although a matter of long-time controversy, de novo BCR-ABL+ AML is now classified as distinct AML subtype. However, current data show that BCR-ABL occur primarily in AML with antecedent myeloid disorder, such as myelodysplasia-related changes [6]. The cytogenetic and molecular abnormalities included in this classification are summarized in **Table 1**.

**223**

*Molecular Monitoring in Acute Myeloid Leukemia Patients Undergoing Matched Unrelated…*

t(8;21) (q22;q22.1) RUNX1-RUNX1T1- AML Favorable

t(9;11)(p21.3;q23.3) MLLT3-KMT2A AML Intermediate t(6;9)(p23;q34.1) DEK-NUP214 AML Adverse

*CEBPA*\$

*Mutated CEBPA is associated with biallelic mutations of the gene, not a single mutation.*

CBFB-MYH11- AML Favorable

GATA2; MECOM Adverse

*AML with mutated NPM1 Favorable if without FLT-ITD* 

**Risk group, as per 2017 ELN** 

**stratification**

*or with FLT-ITD low Intermediate if FLT-ITH high*

*Favorable*

Current AML risk categorization follows the latest 2017 European LeukemiaNet (ELN) recommendations and is based on pretreatment genetic abnormalities. It is designed for risk-adapted treatment approach of patients with AML, conforming to their molecular profiles [7]. Three risk categories are recognized: favorable risk, intermediate risk and adverse risk group [7]. However, the prognostic significance of genetic abnormalities should be only analyzed in association/codependence with other patient-related or disease-related prognostic factors. Increasing age is correlated with poor prognosis for two reasons; not only the poorer performance status in older age groups and the increased risk of toxicity and treatment-related mortality, but also the increased probability of previous underlying malignancy such as MDS or MPN, associated with adverse cytogenetic and higher risk of treatment resistance. Furthermore, the presence of two genetic abnormalities simultaneously and their interactions can result in different prognostic impact, depending on the presence or the absence of another. The best studied example is the NPM1-FLT3-ITD interaction. As shown in **Table 1**, mutated NPM1 in the absence of a *FLT3*-ITD or presence of *FLT3*-ITD with a low allelic ratio is related to favorable prognosis, while the high allelic ratio of *FLT3*-ITD relocates it in the intermediate risk group. To the contrary, not mutated NPM1, or wild-type NPM1 in the absence of a *FLT3*-ITD or low allelic ratio *FLT3*-ITD is considered as intermediate risk group and finally, wildtype NPM1 plus high allelic ratio of *FLT3*-ITD carries adverse prognosis [8]. ELN risk categories are presented in **Table 1** in association with WHO classification of AML. In addition to those abnormalities, mutations in RUNX1, mutations in ASXL1 and in TP53 convey particularly poor prognosis [9]. In regards to AML-karyotype, complex karyotypes and monosomal karyotypes, specific aneuploidies, such as deletion of chromosome 5 and chromosome 7 or 5q, 7q deletion, predict adverse prognosis in AML patients. These are often associated with TP53 mutations [10].

*AML with biallelic mutations of* 

*\*Inv(3)(q21.3q26.2) results in reposition of a distal GATA2 enhancer to activate MECOM expression, not a fusion* 

*Recurrent cytogenetic and molecular abnormalities in AML (4th revision of WHO classification, published in* 

*DOI: http://dx.doi.org/10.5772/intechopen.94830*

**WHO classification 2017**

inv(16)(p13.1q22) or t(16;16)

inv(3)(q21.3q26.2) or t(3;3)

(p13.1;q22)

(q21.3;q26.2)\*

*gene. \$*

**Table 1.**

**AML with recurrent genetic abnormalities adapted from 4th revised** 

**Cytogenetic abnormality Molecular abnormality**

t(1;22)(p13.3;q13.3) RBM15-MKL1

**1.3 AML risk categories**

*2017) and ELN risk categories.*

*Molecular Monitoring in Acute Myeloid Leukemia Patients Undergoing Matched Unrelated… DOI: http://dx.doi.org/10.5772/intechopen.94830*


*\*Inv(3)(q21.3q26.2) results in reposition of a distal GATA2 enhancer to activate MECOM expression, not a fusion gene.*

*\$ Mutated CEBPA is associated with biallelic mutations of the gene, not a single mutation.*

#### **Table 1.**

*Acute Leukemias*

**1. Introduction**

**1.1 Acute myeloid leukemia (AML)**

characterize the AML subtype [1].

topoisomerases, or prior radiotherapy [4].

**1.2 WHO classification of AML**

than 65 [2, 3].

Acute myeloid leukemia (AML) is a heterogeneous malignant disease of the hematopoietic system, marked by mutational arrest of myeloid lineage precursor cells and limited myeloid differentiation capacity [1]. Theoretically, malignant transformation can arise at any level at which cell precursors are capable of selfrenewal. However, the hematopoietic precursors are typically arrested in the earliest stages of myeloid maturation pathway - myeloblasts or promyelocytes. The malignant cells suppress the normal hematopoiesis by accumulating in the bone marrow and displacing the normal hematopoietic stem cells, resulting in depletion of normal blood cells. Тhe presence of more than 20% myeloblasts in the bone marrow or peripheral blood, as assessed by morphological evaluation of blood smears and bone marrow aspirate smears is diagnostic for AML. Morphologically, AML cells resemble normal myeloblasts to some extent, although they are distinguished by specific features, such as Auer Bodies – crystalloid azurophylic granules or Auer Rods – needle-shaped conglomerates of granules. Immunophenotyping, cytogenetics and molecular genetics must be employed to confirm the diagnosis of AML and further

AML is one of the most common types of leukemia in adults, as stated by American Society of Cancer, the second most common, following chronic lymphocytic leukemia (CLL), but the leading cause of mortality of leukemic deaths [2]. The median age at diagnosis is approximately 70 years. The estimated annual age-standardized incidence rate is 4.3 per 100.000, more precisely, from 1.3 per 100.000 in patients younger than 65 years and 12.2 per 100.000 in patients older

The etiology of de novo cases of AML is quite obscure. Only a small portion of all AML cases - around 10%, are secondary AML, due to transformation of prior hematological malignancy, such as myelodisplastic syndrome (MDS) or myeloproliferative neoplasm (MPN). Around another 10% of all cases arise from suggested DNA damage of known previous factor, as prior therapy with alkylating agents or

The revised fourth revision to the World Health Organization classification of Tumors of Hematopoietic and Lymphoid Tissues, published in 2017, distinguishes six AML subtypes and it incorporates cytogenetic and molecular abnormalities into diagnostic algorithms, in contrast to previous classifications of AML, based on morphology and immunophenotype [5]. The entity "AML with recurrent genetic abnormalities" comprises 11 subcategories of AML, with acute promyelocitic leukemia (APL with PML-RARA) included. The abnormalities that are not included in this group are considered to be rare among adult population. Six well-defined recurrent balanced translocations and inversions and their variants are covered within this classification. Two entities included are new provisional subcategories: AML with *BCR-ABL1* fusion gene and AML with mutated *RUNX1*. Although a matter of long-time controversy, de novo BCR-ABL+ AML is now classified as distinct AML subtype. However, current data show that BCR-ABL occur primarily in AML with antecedent myeloid disorder, such as myelodysplasia-related changes [6]. The cytogenetic and molecular abnormalities included in this classification are

**222**

summarized in **Table 1**.

*Recurrent cytogenetic and molecular abnormalities in AML (4th revision of WHO classification, published in 2017) and ELN risk categories.*

#### **1.3 AML risk categories**

Current AML risk categorization follows the latest 2017 European LeukemiaNet (ELN) recommendations and is based on pretreatment genetic abnormalities. It is designed for risk-adapted treatment approach of patients with AML, conforming to their molecular profiles [7]. Three risk categories are recognized: favorable risk, intermediate risk and adverse risk group [7]. However, the prognostic significance of genetic abnormalities should be only analyzed in association/codependence with other patient-related or disease-related prognostic factors. Increasing age is correlated with poor prognosis for two reasons; not only the poorer performance status in older age groups and the increased risk of toxicity and treatment-related mortality, but also the increased probability of previous underlying malignancy such as MDS or MPN, associated with adverse cytogenetic and higher risk of treatment resistance. Furthermore, the presence of two genetic abnormalities simultaneously and their interactions can result in different prognostic impact, depending on the presence or the absence of another. The best studied example is the NPM1-FLT3-ITD interaction. As shown in **Table 1**, mutated NPM1 in the absence of a *FLT3*-ITD or presence of *FLT3*-ITD with a low allelic ratio is related to favorable prognosis, while the high allelic ratio of *FLT3*-ITD relocates it in the intermediate risk group. To the contrary, not mutated NPM1, or wild-type NPM1 in the absence of a *FLT3*-ITD or low allelic ratio *FLT3*-ITD is considered as intermediate risk group and finally, wildtype NPM1 plus high allelic ratio of *FLT3*-ITD carries adverse prognosis [8]. ELN risk categories are presented in **Table 1** in association with WHO classification of AML. In addition to those abnormalities, mutations in RUNX1, mutations in ASXL1 and in TP53 convey particularly poor prognosis [9]. In regards to AML-karyotype, complex karyotypes and monosomal karyotypes, specific aneuploidies, such as deletion of chromosome 5 and chromosome 7 or 5q, 7q deletion, predict adverse prognosis in AML patients. These are often associated with TP53 mutations [10].
