**4. Co-expression of other mutant genes with FLT 3/ITD & their predictive value**

The duplicated areas are inconsistent in size (between 3 and 400 bp) and also in location, but the resulting product is always rich in tyrosine residues. It is hypothesized that modification of the length of the JM domain, rather than increase of tyrosine chain, causes enhancement of function of FLT3. Furthermore, an activating point mutation has been identified in the JM domain in immature leukemia cell. Mono Mac 1 and Mono Mac6 causes substitution of valine by alanine at position valine 592 (V592A) [62], but this mutation has not yet been reported in

A different group of genetic makeup has been described in the activation loop within the second tyrosine kinase domain of the FLT3 receptor that normally inhibits the binding of adenosine triphosphate and substrate to the kinase domain when the receptor is in a dormant state. Frequently, these involve mutations at aspartic acid 835 (D835) or isoleucine 836 (1836)

FLT3-ITD mutations are present in 20–25% of adult patients with AML and correlate with higher WBC count at diagnosis, increased relapse risk, and poor prognosis*.* Moreover, simultaneous loss of the wild-type FLT3 allele is associated with significantly inferior outcome and decreased overall survival in FLT3-ITD patients*.* In pediatric AML patients, FLT3-ITD is detected in 11–16% of cases and linked to worse prognosis [30, 63–65]*.* FLT3-ITD mutations more frequently occur in acute prolymphocytic leukemia (30–39%) containing t(15;17), which produces the PML-RARα oncogene. FLT3-ITD receptors are characterized by ligand-independent receptor dimerization and phosphorylation, but the accurate mechanism of this mutation binding and how it causes constitutive kinase activity has not yet been fully elucidated. Both lengthening as well as

Structural analysis of the EphB2 RTK, it described that JM domain takes up a z-helical conformation, which inhibits the activation of kinase and also self-dimerization. FLT3-ITD would affect the hindrance of kinase domain and, with the help of JM domain, would produce auto phosphorylation. In further studies of HSCT bone marrow cells in mice which done by retro virally transduced with FLT3-ITD, which produced oligo clonal band of MPD due to onco-

Activating TKD mutations are noticed in 7–14% of adults with AML, but D835 has no significant correlation with poor outcome. In pediatric group this mutation was observed 3–8%. Clustering algorithms has identified that childhood acute leukemias carrying rearrangements of MLL gene on chromosome 11q23 show overexpression of wild-type FLT3 mRNA easily distinguishing them from conventional pre-B ALL and AML. Interestingly, FLT3-TKD deletions involving codons D835 and I836 were identified more frequently with MLL gene [67, 68]. Patient with

Like FLT3-ITD receptors, FLT3-TKD mutations stimulate ligand-independent receptor activation and promote growth factor independence in 32D cells. However, it is under evaluation

these activating FLT3-TKD alterations expresses higher levels of FLT3 transcripts [69].

shortening of the JM domain result in activation of FLT3 receptor [65]*.*

genic potential of FLT3 ITD mutation [66].

**3.11. TKD mutations**

primary AML blasts.

in exon 20.

72 Myeloid Leukemia

**3.10. FLT3-ITD**

#### **4.1. Prognostic and predictive value of the NPM1, FLT3, and CEBPA genotypes**

NPM1 mutation or combined genotype NPM1mut/FLT3-ITDneg is reported as a favorable prognostic marker for attainment of a complete remission after induction therapy [70–73]. Actually, no data is available for specific chemotherapy for NPM1mut [74].

In a more recent study, NPM1 was shown to act as a co-repressor in retinoic acid-associated transcriptional regulation in a manner such that during retinoic acid-induced cellular differentiation, activating protein transcription factor 2 (AP2) recruits NPM1 to the promoter of certain retinoic acid-responsive genes. The German-Austrian AML Study Group (AMLSG) reported favorable effect of ATRA if given with conventional chemotherapy on complete remission rate, event-free survival, and OS in elderly patients with (non- APL) AML1 [50]. This study finding was coinciding with retrospective data in which beneficial effect of ATRA was restricted to NPM1mut/FLT3-ITDneg patients [75]. So, the genotype NPM1mut/FLT3- ITDneg appears as a predictive genotypic marker for the valuable effect of ATRA in non-APL AML.

FLT3-ITD has been reported consistently as an unfavorable prognostic marker for RFS and OS. Whether other molecular markers, in particular NPM1mut, add to prognostication in FLT3-ITDpos, AML is unclear [76, 77]. It is reported in some studies that genotype NPM1mut/ FLT3-ITDpos shows more favorable prognosis compared with the genotype NPM1WT/FLT3- ITDpos; however, confirmation by other studies are due now [56]. More recent data give insight that outcome is also related to the concentration of the mutant allele and not just its mere presence [77]. However, if NPM1 mutation status was included to the prognostic model, the mutant wild-type ratio of FLT3-ITD was not an important prognostic factor. Currently in randomized multicenter phase III trial [Cancer and Leukemia Group B (CALGB) 10603; clinicaltrials.gov, NCT00651261] wild-type ratio (high versus low) is applied for midostaurin (PKC412) in young adult AML patients.

CEBPA mutations are another genetic abnormality that consistently associated with good prognosis, either in the subset of patients with intermediate-risk cytogenetics or with normal karyotypes [74]. In the context of other molecular markers, the mutated CEBPA alone retained its prognostic significance for RFS and OS; additional mutations did not affect outcome in the CEBPA mut subgroup. This needs validation. Actually, even in the largest cohort of patients analyzed so far in CN-AML, the sample size in the CEBPA mut subgroup was too low for meaningful analysis, in particular to compare the different post-remission strategies (chemotherapy versus autologous SCT versus allogeneic SCT) [74]. Therefore, the prognostic marker CEBPA mut cannot actually be used as a predictive marker.

**5.1. Induction therapy**

allogeneic HSCT [81].

**5.3. Response assessment**

not changed much over the years.

**5.2. Post-remission consolidation chemotherapy**

**5.4. Response assessment during follow-up period**

2 years and then every 3–6 months up to 5 years [77].

**5.5. Role of HSCT as a consolidation strategy**

individual trial design) no further treatment.

The primary objective of induction therapy is attainment of normal bone marrow function. The criteria of CR are a platelet count of >100 × 109/L, neutrophil count of >1 × 109/L and a bone marrow examination with <5% blasts. Patients with persistent >5% blasts in the bone marrow following induction chemotherapy have a poor overall survival (OS) [79, 80]. Despite multiple trials, the standard remission induction therapy consisting of three daily infusions of an anthracycline and cytarabine given as continuous infusion for 7 days (7 + 3 regimen) has

Genomics of Acute Myeloid Leukemia http://dx.doi.org/10.5772/intechopen.72757 75

After achieving complete remission(CR) after induction therapy, disease relapse is a certainly virtual. Median disease-free survival (DFS) in this circumstance is estimated at only 4–8 months. Options for post-remission consolidation therapy include high-dose chemotherapy

After conventional induction therapy with 3 days of an anthracycline and 7 days of cytarabine ("3 + 7") or other recommended regimens according to guidelines, response assessment is

Repeat bone marrow examination is recommended every 3 months for the first 2 years; in some cases, it continues every 6 months for the following 2–3 years. Most relapses occur within 1–3 years after the completion of treatment. Standardized schedule is necessary if MRD monitoring is advised. Blood counts should be repeated every 1–3 months for the initial

Prospective single institution studies comparing allogeneic HSCT as a consolidation treatment in the 1980s and the early 1990s showed lower relapse rates of 181 and improved DFS with allogeneic HSCT in AML patients in CR1, but none conclusively demonstrated a survival advantage [81]. Subsequently, six cooperative group trials prospectively addressed the role of HSCT in AML in CR1 in 1995 [91]. Patients with HLA-identical sibling donors were offered allogeneic transplantation ("Genetic randomization"). Remaining patients were randomized to autologous transplantation, intensive consolidation chemotherapy (ICC) or (depending on

Among these trials, the landmark European Organization for Research and Treatment of Cancer (EORTC)-Gruppo Italiano Malattie Ematologiche Maligne dell'Adulto (GIMEMA) trial showed superior 4-year leukemia-free survival (LFS) with allogeneic (55%) and autologous

commonly performed between day 21 and 28 after the start of therapy [81].

MLL partial tandem duplication (PTD) is exclusively found in normal karyotype (CN)-AML with an incidence reported from 5% to 11%. There are no clinical features differentiating MLL-PTD positive versus MLL wild-type patients [78]. Approximately 30–40% of MLL-PTDpositive patients consist of FLT3-ITD mutations, whereas combined existence of CEBPA with NPM1 mutations is rare. MLL-PTD is linked with shorter complete remission duration or worse RFS; however, in these studies, MLL-PTD did not show any effect on OS [77]. Recently, the CALGB reported relationship of MLL-PTD in young adults who received autologous SCT in the first complete remission. Clinical outcomes between the MLL-PTD-positive and the MLL wild-type groups were equivalent. WT1 mutations were reported in 10–12.6% in CN-AML. However, variable results have been mentioned about the prognostic significance of WT1 mutations. Both CALGB and MRC studies reported the prognostic impact of WT1 mutations in young adults with CN-AML. In both studies, patients with WT1 mutations were an independent adverse prognostic factor with inferior RFS and OS in multivariate analysis. This is in contrast to the findings of Gaidzik et al. who did not observe any decreased RFS and OS in relation with WT1 mutations on RFS and OS neither in univariate nor multivariate analysis. Of note, when performing exploratory subset analysis on FLT3-ITD samples, the WT1mut/FLT3-ITD pos genotype appeared to be associated with worse clinical course. One major difference between the three studies is different doses of cytarabine used. Cumulative dose of cytarabine was significantly higher in the trial reported by Gaidzik et al. (in preparation), suggesting that the negative impact ofWT1 mutations reported by others may be overcome by the use of high-dose cumulative cytarabine. On the basis of the current data, the prognostic impact of WT1 mutation remains unclear and its impact on treatment remains to be elucidated in future studies.

Although the majority of studied related to CN patients contained at least one of the already mentioned genetic alterations. In a study of AML done by one group, almost a quarter of patients did not have FLT3-ITD, FLT3-TKD, MLL-PTD, or mutations in the CEBPA or NPM1 genes [77]. Thus, it is likely that unidentified novel gene mutations and/or abnormal gene expression with prognostic significance will be discovered in the future. Expression of the meningioma 1 (MN1) gene might become such a novel prognostic factor. Same group in study reported also high expression of the MN1 gene related to inferior RFS and OS and a higher risk of relapse in CN aged 60 years or younger with de novo or secondary AML. This observation needs confirmation before implementation.
