Clinical impact of FLT3 mutation load in acute promyelocytic leukemia with t(15;17)/PML-RARA

Effective treatment with Gilteritinib-based regimens for FLT3-mutant extramedullary relapse in acute promyelocytic leukemia

OBJECTIVE

Extramedullary relapse (EMR) is rare in acute promyelocytic leukemia (APL) and, there is a lack of information on its management. Current practices for EMR in APL are always to adopt strategies from other subtypes of Acute lymphoblastic leukemia (ALL) and Acute myeloid leukemia (AML). Gilteritinib, a highly selective FLT3 inhibitor, has demonstrated a remarkable effect on EMR in FLT3-mutant AML. Therefore, it is worthwhile exploring if FLT3 mutation can be a therapeutic target and assessing the efficacy of Gilteritinib on FLT3-mutant EMR in APL.

METHODS

We described three cases of FLT3-mutant EMR in APL, comprising two isolated EMR cases and one systemic relapse. The patients underwent treatment with Gilteritinib-based regimens based on FLT3 mutation.

RESULTS

All three patients achieved complete regression of EMR, and no signs of tumor lysis syndrome during Gilteritinib-based therapy, only patient 1 showed mild granulocytopenia. They all maintained molecular complete remission (mCR) during the follow-up period.

CONCLUSIONS

The Gilteritinib-based regimen shows a high and sustained therapeutic effect with minimal adverse effects, and provides a valuable experience for further evaluation in EMR APL patients.

Flexible genosensors based on polypyrrole and graphene quantum dots for PML/RARα fusion gene detection: A study of acute promyelocytic leukemia in children

Acute promyelocytic leukemia (APL) in children is associated with a favorable initial prognosis. However, minimal residual disease (MRD) follow-up remains poorly defined, and relapse cases are concerning due to their recurrent nature. Thus, we report two electrochemical flexible genosensors based on polypyrrole (PPy) and graphene quantum dots (GQDs) for label-free PML-RARα oncogene detection. Atomic force microscopy (AFM), scanning electron microscope (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to characterize the technological biosensor development. M7 and APLB oligonucleotide sequences were used as bioreceptors to detect oncogenic segments on chromosomes 15 and 17, respectively. AFM characterization revealed heterogeneous topographical surfaces with maximum height peaks for sensor layers when tested with positive patient samples. APLB/Genosensor exhibited a percentage change in anode peak current (ΔI) of 423 %. M7/Genosensor exhibited a ΔI of 61.44 % for more concentrated cDNA samples. The described behavior is associated with the biospecific recognition of the proposed biosensors. Limits of detection (LOD) of 0.214 pM and 0.677 pM were obtained for APLB/Genosensor and M7/Genosensor, respectively. The limits of quantification (LOQ) of 0.648 pM and 2.05 pM were estimated for APLB/Genosensor and M7/Genosensor, respectively. The genosensors showed reproducibility with a relative standard deviation of 7.12 % for APLB and 1.18 % for M7 and high repeatability (9.89 % for APLB and 1.51 % for M7). In addition, genetic tools could identify the PML-RARα oncogene in purified samples, plasmids, and clinical specimens from pediatric patients diagnosed with APL with high bioanalytical performance. Therefore, biosensors represent a valuable alternative for the clinical diagnosis of APL and monitoring of MRD with an impact on public health.

The treatment of acute promyelocytic leukemia in 2023: Paradigm, advances, and future directions

The transformation of acute promyelocytic leukemia (APL) from an often fatal to highly curable cancer with long-term survival exceeding 90% is one of the greatest and most inspiring successes in oncology. A deeper understanding of the pathogenesis of APL heralded the introduction of highly effective therapies targeting the mutant protein that drives the disease, leading to the chemotherapy-free approach to cure almost all patients. In this review, we discuss the paradigm of treatment of APL in 2023, reinforce the high risk of early death without prompt initiation of treatment at first clinical suspicion, and dedicate a special focus to novel agents and future directions to improve cure rates and quality of life in patients affected by APL.

Discovery of druggable cancer-specific pathways with application in acute myeloid leukemia

An individualized cancer therapy is ideally chosen to target the cancer's driving biological pathways, but identifying such pathways is challenging because of their underlying heterogeneity and there is no guarantee that they are druggable. We hypothesize that a cancer with an activated druggable cancer-specific pathway (DCSP) is more likely to respond to the relevant drug. Here we develop and validate a systematic method to search for such DCSPs, by (i) introducing a pathway activation score (PAS) that integrates cancer-specific driver mutations and gene expression profile and drug-specific gene targets, (ii) applying the method to identify DCSPs from pan-cancer datasets, and (iii) analyzing the correlation between PAS and the response to relevant drugs. In total, 4,794 DCSPs from 23 different cancers have been discovered in the Genomics of Drug Sensitivity in Cancer database and validated in The Cancer Genome Atlas database. Supporting the hypothesis, for the DCSPs in acute myeloid leukemia, cancers with higher PASs are shown to have stronger drug response, and this is validated in the BeatAML cohort. All DCSPs are publicly available at https://www.meb.ki.se/shiny/truvu/DCSP/.

'FLT3-ITD Mutation Does Not Influence Survival Outcome in Adult Acute Promyelocytic Leukemia Patients Treated With ATO and ATRA-Based Therapeutic Regimen: Experience From a North Indian Tertiary Care Centre'

INTRODUCTION

NPM1 and FLT3-ITD are frequently mutated genes in acute myeloid leukemia. We studied clinico-hematological profile and survival outcome of adult acute promyelocytic leukemia (APL) patients harboring these mutations.

MATERIALS AND METHODS

De novo APL cases (> 12 years), enrolled between January 2019 and June 2020, were evaluated for FLT3-ITD and NPM1 mutations (A, B, D mutations) by conventional and real-time qualitative PCR respectively.

RESULTS

FLT3-ITD mutation was detected in 12 of 36 (33.3%) de novo APLs cases while NPM1 mutation was not detected. FLT3-ITD was more frequently associated with Sanz high-risk category as compared to the intermediate-risk category (75% vs. 29%, P = .02), with BCR3 transcript type (P = .08) and higher median WBC count [22.7 × 10⁹/L)(range 1.3-184), P = .018]. One and half-years overall survival (OS) and event-free survival (EFS) were not significantly altered by the presence/absence of FLT3-ITD mutation (OS 86% vs. 70%, P = .32; EFS 86% vs. 70%, P = .33), between genders (OS, EFS both 89% in males vs. 69% in females, P = .15) and between adolescent and younger adults (AYA) (≤ 30 years) and older adult APL cases (> 30 years) (OS 86% vs. 78%, P = .55; EFS 85% vs. 77%, P = .55), however were significantly lower with BCR3 transcript as compared to BCR1 transcript (OS 56% vs. 91%, P = .019; EFS 56% vs. 91%, P = .016) in univariate analysis, although not in multivariate analysis. One and half-year OS and EFS was 57% (6/14, P = .009 for each) in high-risk APL.

CONCLUSION

FLT3-ITD mutation did not influence survival outcome in adult APL treated with ATO and ATRA-based therapeutic regimen.

Thrombocytosis in a patient with acute promyelocytic leukemia during treatment with all-trans retinoic acid and arsenic trioxide

Thrombocytosis is an unusual side effect of all-trans retinoic acid (ATRA) treatment that occurs in some patients with acute promyelocytic leukemia (APL).

FLT3-ITD Allelic Burden and Acute Promyelocytic Leukemia Risk Stratification

The significance of FLT3-ITD in acute promyelocytic leukemia (APL) is not well-established. We performed a bi-center retrospective study of 138 APL patients, 59 (42.8%) of whom had FLT3-ITD. APL patients with FLT3-ITD had higher baseline white blood cell counts (WBCs) (p < 0.001), higher hemoglobin, (p = 0.03), higher aspartate aminotransferase (p = 0.001), lower platelets (p = 0.004), lower fibrinogen (p = 0.003), and higher incidences of disseminated intravascular coagulation (p = 0.005), M3v variant morphology (p < 0.001), and the bcr3 isoform (p < 0.001). FLT3-ITD was associated with inferior post-consolidation complete remission (CR) (p = 0.02) and 5-year overall survival (OS) of 79.7%, compared to 94.4% for FLT3-WT (wild-type) (p = 0.02). FLT3-ITD was strongly associated with baseline WBCs ≥ 25 × 10⁹/L (odds ratio (OR): 54.4; 95% CI: 10.4-286.1; p < 0.001). High FLT3-ITD allelic burdens correlated with high-risk (HR) Sanz scores and high WBCs, with every 1% increase in allelic burden corresponding to a 0.6 × 10⁹/L increase in WBC. HR APL was associated with a 38.5% increase in allelic burden compared with low-risk (LR) APL (95% CI: 19.8-57.2; p < 0.001). Our results provide additional evidence that FLT3-ITD APL is a distinct subtype of APL that warrants further study to delineate potential differences in therapeutic approach.

Analysis of FLT3-Activating Mutations in Patients With Acute Myelogenous Leukemia in Jordan: Association With FAB Subtypes and Identification of Subgroups With Poor Prognosis

BACKGROUND

FLT3 mutations are common in acute myeloid leukemia (AML), particularly in French-American-British M2 subtype AML and in cytogenetically normal (CN) AML; however, its incidence in Jordan is poorly studied. An FLT3 mutation implies poor prognosis in AML patients. We aimed to assess the incidence and prognostic value of FLT3 mutations in AML in Jordan.

PATIENTS AND METHODS

One hundred thirty-two newly diagnosed unselected AML patients were included. Patient data were collected, including demographics as well as morphologic, cytogenetic, and molecular testing results. FLT3 mutations were detected by real-time reverse transcriptase PCR, next-generation sequencing, or both. Survival analysis and comparisons of incidence, remission rate, relapse, and survival outcomes between FLT3-mutated and wild-type groups were done and prognostic factors identified.

RESULTS

FLT3 mutation was detected in 40% of AML patients. The highest incidence was associated with M2 subtype AML (47%) and CN-AML (50%). There was a significant negative association between FLT3 mutations and overall survival (OS), as well as a trend toward improved relapse-free survival, with 3-year OS being 19.17% vs 34.16% (P < .0001) and 33.6% vs 71.0% (P = .085), respectively. Patients with FLT3 mutation had a significantly better complete remission rate after induction (67.9% vs 63.3%, P = .001). Also, OS improved in patients with complete remission (P = .0015) and who then continued to allogeneic hematopoietic cell transplantation compared to FLT3 wild-type patients (P < .001).

CONCLUSION

FLT3 mutation is common in Jordanian AML patients, with the highest incidence occurring in patients with M2 or CN disease. It implies a poor prognosis, with poor OS and relapse-free survival, which may be abrogated by early allogeneic transplantation and/or peritransplantation provision of FLT3 inhibitors.

Combined Expression of CD34 and FLT3-Internal Tandem Duplication Mutation Predicts Poor Response to Treatment in Acute Myeloid Leukemia

Background

Acute myeloid leukemia (AML) is a common hematological malignancy associated with different cytogenetic and genetic abnormalities.

Methods

FLT3-internal tandem duplication (FLT3/ITD) mutation and CD34 expression levels were assessed in the bone marrow (BM) aspirates of 153 de novo AML patients. Data were correlated with relevant clinic-pathological features of the patients, response to treatment, disease-free survival (DFS), and overall free survival (OS) rates.

Results

FLT3-ITD mutation was detected in 27/153 (17.6%) AML patients (P=0.001), and CD34 was expressed in 83/153 (54.2%) patients (P=0.293) compared to those with wild FLT3 and CD34⁻ expression, respectively. Patients with FLT3-ITD mutation showed increased peripheral blood and BM blast cells, abnormal cytogenetics, poor DFS and OS compared to those with wild FLT3 (P=0.013, P<0.001, P=0.010, P=0.008 and P=0.004, respectively), while there was no significant association with response to treatment (P=0.081). There was no significant association between CD34 expression and response to treatment, DFS, and OS (P>0.05). FLT3-ITD mutation and FAB subtypes were independent prognostic factors for DFS. Older age ≥39 years, HB <7 mg/dL PB blast ≥54%, and FLT3-ITD mutation were independent prognostic factors for poor OS in AML patients. The presence of both FLT3-ITD mutation and CD34 expression associated significantly with resistance to therapy (P=0.024), short DFS and OS rates (P=0.006, P=0.037, respectively).

Conclusion

Combined expression of both FLT3-ITD mutation and CD34 expression is an important prognostic and predictive factor for poor disease outcome in AML patients.

Improved outcome in early induction deaths in patients with acute promyelocytic leukemia after therapeutic and supportive interventions: a follow up study of seven-years' experience at a tertiary care center

INTRODUCTION AND OBJECTIVES

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia with characteristic morphology and clinical features. Early mortality rate of 30% has been reported in developed countries despite prompt initiation of treatment. We have previously reported an early induction mortality of approximately 62% in our cohort. Based on this mortality rate, we made changes in our treatment protocol. The objective of this follow-up study was to report the early induction mortality and overall survival of patients with APL after incorporating changes in chemotherapy and supportive care regimen.

SUBJECTS AND METHODS

This was a prospective descriptive study conducted at Aga Khan University Karachi, Pakistan from October 2012 till October 2019. Data of patients included clinical features, morphological findings, cytogenetic and PCR studies, cytotoxic protocols, overall outcome and causes of early induction mortality. The changes in treatment protocol included prophylactic infusion of fresh frozen plasma, dexamethasone therapy and other changes in supportive care regimen. Results were recorded as frequencies and percentages. Statistical Package for the Social Sciences version 19.0 (SPSS Inc., Chicago, IL, USA) was used to analyze patient's data. Survival curves were calculated using the Kaplan-Meier method.

RESULTS

During the study period, total of 447 patients presented with acute myeloid leukemia at our institution out of which 40 patients were diagnosed with acute promyelocytic leukemia (9%). Out of these 40 patients 24 were males and 16 were females. The median age was 37 years. Twenty-five patients were in low risk group whereas 15 were high-risk. Differentiation syndrome was seen in 14 patients. As a part of induction chemotherapy, 13 patients received only ATRA because they were not eligible for chemotherapy and 17 patients received a combination of ATRA and anthracycline. Among the remaining patients, four received ATRA, arsenic and anthracycline while two received ATRA and arsenic only. Four patients did not receive any treatment because of rapid deterioration of clinical condition and death. The overall survival was 65% and early induction mortality was 30%.

CONCLUSION

The early induction mortality decreased to 30% from 62% in this study and the overall survival was 65%. With the introduction of prophylactic infusion of fresh frozen plasma, dexamethasone and appropriate supportive treatment during the induction chemotherapy, we were able to improve the induction mortality and overall survival of patients.

Prognostic Significance of bcr-1 and bcr-3 Isoforms of PML-RARA and FLT3-ITD in Patients With Acute Promyelocytic Leukemia

BACKGROUND

Acute promyelocytic leukemia (APL) has a characteristic peculiar morphologic and genetic features as well as a more favorable outcome. We studied the differential effect of bcr-1 and bcr-3 isoforms of the promyelocytic leukemia/retinoic acid receptor alpha (PML-RARA) transcript together with FLT3 internal tandem duplication (FLT3-ITD) mutation status on the outcome of newly diagnosed de novo APL patients.

PATIENTS AND METHODS

This cohort study included all patients diagnosed with APL at outpatient medical and pediatric oncology clinics of the National Cancer Institute, Cairo University, Cairo, Egypt, from May 2012 to January 2018.

RESULTS

The study included 118 patients with APL, 71 adults (60.2%) and 47 children (39.8%). Median (range) age was 25 (1.5-70) years. Children had significantly higher total leukocyte count (≥10 × 10⁹/L), disseminated intravascular coagulation (DIC), and thrombocytopenia (< 40 × 10⁹/L) than adults (P = .04, .03, and .04, respectively), while the latter group had significantly higher hemorrhage than children (P = .04). FLT3-ITD mutation was detected in the whole group, children, and adults in 23.7%, 30.6%, and 24.6%, respectively. FLT3-ITD mutation was significantly associated with leukocytosis in the whole group (P = .039). bcr-3 was significantly associated with FLT3-ITD mutation in the whole APL cohort and in adults (P = .011, P = .022). All children (both bcr-1 and bcr-3) and all adult patients with bcr-3 experienced CR, while 22 (78.5%) of 28 patients with bcr-1 experienced CR (P = .04). APL patients with DIC and hemorrhage had significantly lower overall survival (P = .002 and < .001, respectively). Overall survival for APL in children was significantly better than in adults (P = .005). Multivariate analysis indicated that age was an independent prognostic variable affecting survival (hazard ratio = 2.6; 95% confidence interval, 1.3-5.3; P = .007) (adults had hazard ratio of death 2.6 times higher than children). DIC and FLT3-ITD were independent prognostic variables affecting survival in children with APL (hazard ratio = 12.3; 95% confidence interval, 1.46-104.61; P = .021; and hazard ratio = 5.2; 95% confidence interval, 1.01-26.95; P = .048, respectively).

CONCLUSION

Age is an independent prognostic factor for APL. bcr-3 is significantly associated with FLT3-ITD in adults with APL. DIC and FLT3-ITD are adverse prognostic factors in children with APL. Despite children being at higher risk, outcome is better than in adults.

FLT3-ITD impedes retinoic acid, but not arsenic, responses in murine acute promyelocytic leukemias

Acute promyelocytic leukemia (APL) is often associated with activating FLT3 signaling mutations. These are highly related to hyperleukocytosis, a major adverse risk factor with chemotherapy-based regimens. APL is a model for oncogene-targeted therapies: all-trans retinoic acid (ATRA) and arsenic both target and degrade its ProMyelocytic Leukemia/Retinoic Acid Receptor α (PML/RARA) driver. The combined ATRA/arsenic regimen now cures virtually all patients with standard-risk APL. Although FLT3-internal tandem duplication (ITD) was an adverse risk factor for historical ATRA/chemotherapy regimens, the molecular bases for this effect remain unknown. Using mouse APL models, we unexpectedly demonstrate that FLT3-ITD severely blunts ATRA response. Remarkably, although the transcriptional output of initial ATRA response is unaffected, ATRA-induced PML/RARA degradation is blunted, as is PML nuclear body reformation and activation of P53 signaling. Critically, the combination of ATRA and arsenic fully rescues therapeutic response in FLT3-ITD APLs, restoring PML/RARA degradation, PML nuclear body reformation, P53 activation, and APL eradication. Moreover, arsenic targeting of normal PML also contributes to APL response in vivo. These unexpected results explain the less favorable outcome of FLT3-ITD APLs with ATRA-based regimens, and stress the key role of PML nuclear bodies in APL eradication by the ATRA/arsenic combination.

Factors Affecting Early Death and Survival of Patients With Acute Promyelocytic Leukemia Treated With ATRA-Based Therapy Regimens

PURPOSE

To perform a retrospective analysis of the prognostic relevance of clinicopathologic parameters in a well-documented cohort of patients treated with all-trans-retinoic acid (ATRA)-based induction regimens in order to discover which indicators can predict a high risk of early death (ED) and patient survival.

PATIENTS AND METHODS

We analyzed data of 288 newly diagnosed adult acute promyelocytic leukemia patients in Hangzhou, China. The median follow-up time was 32 months (range, 6-78 months).

RESULTS

The 3-year disease-free and overall survival rates were 90.83% and 91.69%, respectively. In the multivariable analysis, older age (≥ 60 years) was the only independent risk factor for ED (hazard ratio [HR] = 15.057; P = .004). High white blood cell count was not a risk factor for ED (P = .055), but it was for relapse (HR = 2.7; P = .009). FLT3 mutation (HR = 3.9; 95% confidence interval, 1.4 to 10; P = .007) and older age (≥ 60 years) (HR = 5.3; 95% confidence interval, 2.4 to 11; P < .001) were prognostic factors for poorer disease-free and overall survival. Interestingly, CD15 negativity (HR = 0.23; P = .049) was a prognostic factor for relapse. The ED rate was 5.9% (17/288 patients).

CONCLUSION

The perceived impact of the identification of these high-risk factors should be described in order to decide whether any modifications to treatment strategy should be entertained.

Early mortality in acute promyelocytic leukemia: Potential predictors

Acute promyelocytic leukemia (APL) is a rare leukemia characterized by the balanced reciprocal translocation between the promyelocytic leukemia gene on chromosome 15 and the retinoic acid receptor α (RARα) gene on chromosome 17, and accounts for 10-15% of newly diagnosed acute myeloid leukemia each year. The combined use of all-trans retinoic acid and arsenic trioxide (ATO) as primary therapy has markedly improved the survival rate of patients with APL. Mortality in the first 30 days following therapy remains a major contribution to treatment failure. In the present study, published data was reviewed with a focus on the factors associated with early mortality. When treated with ATO as a primary treatment, the fms-like tyrosine kinase-internal tandem deletion has no impact on early mortality. Low lymphoid enhancer binding factor-1 expression may be a reliable marker for early mortality and the target of therapy if it could be proven by further studies. Cluster of differentiation (CD)56+ and CD34+/CD2+ may be candidates to select high-risk patients. The risk of early mortality in APL still cannot be predicted via the cell surface makers, despite multiple studies on their prognostic significance. Typically, a complex translocation did not alter the survival rate in patients with APL; however, if an abnormal karyotype [e.g., Ide(17), ZBTB16/RARα and STAT5B/RARα] appeared singularly or as part of a complex mutation, there is a high possibility of early mortality if clinicians are unable to identify or monitor it.

The clinical significance of FLT3 ITD mutation on the prognosis of adult acute promyelocytic leukemia

BACKGROUND AND AIMS

To explore the relationship between FLT3 (encoding Fms related tyrosine kinase 3) internal tandem duplication (ITD) mutations with the prognosis of acute promyelocytic leukemia. The PubMed database, the Cochrane Library, conference proceedings, the EMBASE databases, and references of published trials and review articles were searched. Two reviewers independently assessed the quality of the trials and extracted the data. Odd ratios (ORs) for complete remission (CR) rate after induction therapy, 5-year overall survival (OS), and 5-year disease free survival (DFS) were pooled using the STATA package.

MAIN RESULTS

Seventeen trials involving 2252 patients were ultimately analyzed. The pooled OR showed that the FLT3 ITD mutation group had a poor prognosis in terms of CR rate (OR = 0.53, 95% confidence interval (CI), 0.30-0.95, P = 0.03), 5-year OS (OR = 0.47, 95% CI, 0.29-0.75, P = 0.002), and as 5-year DFS (OR = 0.48, 95% CI, 0.29-0.78; p = 0.003).

CONCLUSIONS

The results suggested that FLT3 ITD mutations could become an indicator of poor prognosis of APL, and these patients should receive more intensive therapy according to current guidelines.

Prevalence and Clinical Significance of FLT3 and NPM1 Mutations in Acute Myeloid Leukaemia Patients of Assam, India

Acute Myeloid Leukaemia (AML) is one of the common forms of haematological malignancy in adults. We analysed the prevalence and clinical significance of FMS-like tyrosine kinase 3 (FLT3) and Nucleophosmin 1 (NPM1) mutations in AML patients of North East India. Co-prevalence and clinical significance of three recurrent chromosomal translocations namely t(15; 17), t(8; 21), t(16; 16) and expression of epidermal growth factor receptor (EGFR), flow markers were also documented and co-related with disease progress. We analysed bone marrow aspirates or peripheral blood samples from 165 newly diagnosed AML patients. All clinical samples were analysed by Real Time PCR and DNA sequencing based assays. NPM1 was the most frequently detected mutation in the study population (46/165 = 27.90%, 95% CI 20.75-35.05). FLT3 mutations were detected in 27/165 (16.40%, 95% CI 10.45-22.35) patients with internal tandem duplication (FLT3-ITD) in 24/165 (14.60%, 95% CI 8.91-20.29) and FLT3-D835 in 3/165 (1.80%, 95% CI 0-4.13) patients. NPM1 mutations were associated with a higher complete remission rate and longer overall survival (P < 0.01) compared to FLT3-ITD whereas FLT3-ITD showed adverse impact with poor survival rate (P < 0.01), leukocytosis (P < 0.01) and a packed bone marrow. EGFR expression was more in patients with NPM1 mutation compared to FLT3 mutation (P = 0.09). Patients with FLT3 and NPM1 mutations uniformly expressed CD13 and CD33 whereas CD34 was associated with poor prognosis (P ≤ 0.01) in patients with NPM1 mutation. FLT3-ITD was associated with inferior overall survival. However the clinical significance of FLT3-D835 was not clear due to small number of samples. NPM1 mutation showed better prognosis with increased response to treatment in the absence of FLT3-ITD.

Retinoic acid and arsenic trioxide in the treatment of acute promyelocytic leukemia: current perspectives

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) with a unique morphological appearance, associated coagulopathy and canonical balanced translocation of genetic material between chromosomes 15 and 17. APL was first described as a distinct subtype of AML in 1957 by Dr Leif Hillestad who recognized the pattern of an acute leukemia associated with fibrinolysis, hypofibrinogenemia and catastrophic hemorrhage. In the intervening years, the characteristic morphology of APL has been described fully with both classical hypergranular and variant microgranular forms. Both are characterized by a balanced translocation between the long arms of chromosomes 15 and 17, [t(15;17)(q24;q21)], giving rise to a unique fusion gene PML-RARA and an abnormal chimeric transcription factor (PML-RARA), which disrupts normal myeloid differentiation programs. The success of current treatments for APL is in marked contrast to the vast majority of patients with non-promyelocytic AML. The overall prognosis in non-promyelocytic AML is poor, and although there has been an improvement in overall survival in patients aged <60 years, only 30%-40% of younger patients are still alive 5 years after diagnosis. APL therapy has diverged from standard AML therapy through the empirical discovery of two agents that directly target the molecular basis of the disease. The evolution of treatment over the last 4 decades to include all-trans retinoic acid and arsenic trioxide, with chemotherapy limited to patients with high-risk disease, has led to complete remission in 90%-100% of patients in trials and rates of overall survival between 86% and 97%.

Evolution of a FLT3-TKD mutated subclone at meningeal relapse in acute promyelocytic leukemia

Here, we report the case of an acute promyelocytic leukemia (APL) patient who—although negative for FLT3 mutations at diagnosis—developed isolated FLT3 tyrosine kinase II domain (FLT3-TKD)-positive meningeal relapse, which, in retrospect, could be traced back to a minute bone marrow subclone present at first diagnosis. Initially, the 48-yr-old female diagnosed with high-risk APL had achieved complete molecular remission after standard treatment with all-trans retinoic acid (ATRA) and chemotherapy according to the AIDA (ATRA plus idarubicin) protocol. Thirteen months after the start of ATRA maintenance, the patient suffered clinically overt meningeal relapse along with minute molecular traces of PML/RARA (promyelocytic leukemia/retinoic acid receptor alpha) in the bone marrow. Following treatment with arsenic trioxide and ATRA in combination with intrathecal cytarabine and methotrexate, the patient achieved a complete molecular remission in both cerebrospinal fluid (CSF) and bone marrow, which currently lasts for 2 yr after completion of therapy. Whole-exome sequencing and subsequent ultradeep targeted resequencing revealed a heterozygous FLT3-TKD mutation in CSF leukemic cells (p.D835Y, c.2503G>T, 1000/1961 reads [51%]), which was undetectable in the concurrent bone marrow sample. Interestingly, the FLT3-TKD mutated meningeal clone originated from a small bone marrow subclone present in a variant allele frequency of 0.4% (6/1553 reads) at initial diagnosis. This case highlights the concept of clonal evolution with a subclone harboring an additional mutation being selected as the “fittest” and leading to meningeal relapse. It also further supports earlier suggestions that FLT3 mutations may play a role for migration and clonal expansion in the CSF sanctuary site.

Prevalence and Clinical Significance of FLT3 Mutation Status in Acute Myeloid Leukemia Patients: A Multicenter Study

BACKGROUND AND AIMS

FLT3-ITD mutations in acute myeloid leukemia (AML) are associated with a poor prognosis. In Latin America, little epidemiological data exist about these mutations and their influence on clinical evolution and prognosis. Standardization and well-established clinical correlation make FLT3 mutational analysis by molecular methods an invaluable tool to decide among treatment options and to determine AML prognosis.

METHODS

We assessed the prevalence of FLT3-ITD mutations in 138 patients with AML at four hematology referral centers from Mexico and Colombia. Molecular methods based on polymerase chain reaction (PCR) were employed for determining FLT3-ITD status.

RESULTS

Mutations were present in 28 patients indicating a prevalence of 20.28%. Median age was 47 years (5-96). The FLT3 mutation positive group was older, had higher WBC and hemoglobin values and lower platelet counts but without statistical significance. A not previously described mutation in the FLT3 gene was found in one patient involving a nucleotide exchange of timine for cytosine at the 66608 position. A high mortality was found in the FLT3-mutated group, 67.8 vs. 42.72% in the non-mutated group and median survival was 4.9 months vs. 20.4 months, p = 0.009. A mutated FLT3 did not confer poor prognosis to those with M3 AML. The mutated FLT3 population had poor overall survival (OS) despite hematoprogenitor stem cell transplantation (HSCT).

CONCLUSION

Prevalence of FLT3-ITD mutation in AML was present in a proportion comparable to other populations and, when present, was associated with a very poor prognosis.

Significance of ETV6 rearrangement in acute promyelocytic leukemia with t(15;17)/promyelocytic leukemia/retinoic acid receptor alpha

Acute promyelocytic leukemia (APL) is a common subtype of acute myeloid leukemia in China. Since the application of arsenic trioxide and all-trans retinoic acid in the treatment of APL, the prognosis has greatly improved. However, ~20% of patients with APL relapse upon completing chemotherapy. Decreasing the relapse rate and incidence of early mortality may pose the greatest challenges for the future management of APL. Recently, Ets variant 6 (ETV6) was reported to be involved in a variety of translocations associated with hematological malignancies of myeloid and lymphoid origin. To date, little is known about the clinical implication of ETV6 rearrangement in APL. In the present study, ETV6 rearrangement was examined by split-signal fluorescence in situ hybridization in 258 adults with APL, and its association with the clinical features and outcomes of the patients was analyzed. The data suggested that ETV6 rearrangement may be an independent unfavorable prognostic factor for overall survival in APL patients.

Acute promyelocytic leukemia harbouring rare FLT3-TKD and WT1 mutations: A case report

The involvement of the central nervous system (CNS) is rare in acute promyelocytic leukemia (APL). The present study reported the case of a 34-year-old male patient with APL that possessed a rare point mutation (p.Asn841Gly, c.2523C>A) in the tyrosine kinase domain of the FMS-like tyrosine kinase 3 (FLT3) gene and a novel Wilm tumor gene mutation (c.1209_1210insT/p.K404X). The patient suffered central nervous system and systemic relapses twice during systemic and intrathecal chemotherapy. At present, the patient is undergoing alternative induction and consolidation therapies, including the administration of FLT3 inhibitor, tetraarsenic tetrasulfide and novel cytotherapy, and is prepared for salvage allogeneic hematopoietic stem cell transplantion (allo-HSCT). The present study indicated that patients with APL that are at a high risk of relapse and unfavorable gene mutations should receive immediate allo-HSCT, whenever possible.

Lymphoid enhancer binding factor-1 (LEF1) expression as a prognostic factor in adult acute promyelocytic leukemia

Lymphoid enhancer-binding factor 1 (LEF1) is a downstream effector of the Wnt/ β-catenin signaling pathway. High LEF1 expression has been reported as a prognostic marker in hematologic malignancies. We evaluated the prognostic significance of LEF1 expression in 78 adult acute promyelocytic leukemia (APL) patients. APL samples were dichotomized at the median value and divided into: LEF1^low and LEF1^high. LEF1^high patients had lower WBC counts at baseline and were less likely to carry a FLT3 -ITD than LEF1^low patients. Early death occurred only in the LEF1^low group. Moreover, LEF1^low expression was associated with a high Sanz score. Survival analysis of 61 APL patients < 60 years revealed that the LEF1^high group had a significantly longer overall survival (OS). Cox analysis for OS confirmed only LEF1 expression as an independent prognostic factor. Of the 17 patients over the age of 60, those in the LEF1^high group showed a higher median survival. In silico analysis identified 9 differentially expressed, up-modulated genes associated with a high expression of LEF1; the majority of these genes is involved in the regulation of apoptosis. Our study provides evidence that LEF1 expression is an independent prognostic factor in APL, and could be used in patients risk stratification.

AML with gain of chromosome 8 as the sole chromosomal abnormality (+8sole) is associated with a specific molecular mutation pattern including ASXL1 mutations in 46.8% of the patients

Trisomy 8 is the most frequent cytogenetically gained aberration in AML. We compared 79 adult de novo AML with trisomy 8 as the sole cytogenetic abnormality (+8sole) to 511 normal karyotype AML patients (NK). +8sole patients were older (p=0.013), presented lower WBC counts (p=0.010), harbored more often ASXL1 mutations (p<0.001) and RUNX1 mutations (p=0.009), but less frequent FLT3-ITD (p=0.038), NPM1 mutations (p<0.001) and double-mutated CEBPA (p=0.038) than NK patients. No prognostic difference was found between +8sole and NK. With respect to genetic stability we found +8sole was instable, and molecular markers were either stable or gained in number and diversity.

Correlation between FLT3-ITD status and clinical, cellular and molecular profiles in promyelocytic acute leukemias

Internal tandem duplications (ITD) of FLT3 gene occur in about a third of acute promyelocytic leukemias (APL). We investigated the patterns of blood count, surface antigen, expression, chromosome aberrations, PML-RARa isoform, gene expression profile (GEP) and survival in 34 APL patients according to FLT3-ITD status. 97% had a t(15;17) and all of them carried PML-RARa gene fusion, 8 (23.5%) had a FLT3-ITD mutation. Presence of ITD was associated with higher Hb and WBC levels, bcr3 isoform, CD34 expression, CD2 or CD2/CD34 expression. In a multivariate analysis, Hb>9.6g/dL and WBC≥20 × 10(9)/L were important factors for predicting ITD presence. GEP showed that FLT3-ITD carriers clustered separately, even when as few as 5 genes were considered. This study provides further evidence that FLT3-ITDs carriers constitute a biologically distinct group of APL patients.

Analysis for loss of heterozygosity on chromosome arm 13q by STR analysis or SNP sequencing can replace analysis of FLT3-ITD to detect patients with prognostically adverse AML

We aimed at developing novel assays for Loss of Heterozygosity (LOH) detection on 13q as a substitute for FLT3-ITD analysis to identify acute myeloid leukemia (AML) patients with high risk of shorter survival. To this aim, we first analyzed a selected cohort of 185 patients with (n = 138) or without (n = 47) FLT3-ITD by short tandem repeat (STR) analysis for 13q LOH. In 46 of 138 FLT3-ITD positive cases, a FLT3-ITD/FLT3wt ratio of ≥ 1 was measured indicating LOH. Applying analysis with a combination of five different STR markers, a threshold of an STR allelic ratio of >65% allows the identification of LOH in 40/46 (87%) samples. Survival analysis revealed significantly inferior outcome in patients with LOH as detected by STR analysis (event free survival (EFS): no LOH: 13.3 months versus LOH: 4.5 months, p < 0.001; overall survival (OS): no LOH: 35.8 months versus LOH: 9.7 months, p = 0.001). In multivariate Cox regression analysis, 13q LOH was found to be an independent adverse parameter for EFS and OS (p = 0.003 and p < 0.001, respectively) besides age and white blood cell count. Thus, the prognostic impact of 13q LOH is nearly identical to the one of FLT3-ITD/FLT3wt load of ≥ 1 and thus is a feasible alternative to identify respective patients with high risk AML. In a second approach, a cohort of 91 patients was subjected to a proof-of-principle study of applying single nucleotide polymorphism analysis by next generation amplicon sequencing for detection of LOH. 53/91 cases had LOH and 50 were identified with this new method resulting in a positive detection rate of 94.3%.

Immunophenotypes and immune markers associated with acute promyelocytic leukemia prognosis

CD2+, CD34+, and CD56+ immunophenotypes are associated with poor prognoses of acute promyelocytic leukemia (APL). The present study aimed to explore the role of APL immunophenotypes and immune markers as prognostic predictors on clinical outcomes. A total of 132 patients with de novo APL were retrospectively analyzed. Immunophenotypes were determined by flow cytometry. Clinical features, complete remission (CR), relapse, and five-year overall survival (OS) rate were assessed and subjected to multivariate analyses. The CD13+CD33+HLA-DR-CD34− immunophenotype was commonly observed in patients with APL. Positive rates for other APL immune markers including cMPO, CD117, CD64, and CD9 were 68.7%, 26%, 78.4%, and 96.6%, respectively. When compared with patients with CD2− APL, patients with CD2+ APL had a significantly higher incidence of early death (50% versus 15.7%; P = 0.016), lower CR rate (50% versus 91.1%; P = 0.042), and lower five-year OS rate (41.7% versus 74.2%; P = 0.018). White blood cell (WBC) count before treatment was found to be the only independent risk factor of early death, CR failure, and five-year mortality rate. Flow cytometric immunophenotype analysis can facilitate prompt APL diagnosis. Multivariate analysis has demonstrated that WBC count before treatment is the only known independent risk factor that predicts prognosis for APL in this study population.

Prognostic impact of KMT2E transcript levels on outcome of patients with acute promyelocytic leukaemia treated with all-trans retinoic acid and anthracycline-based chemotherapy: an International Consortium on Acute Promyelocytic Leukaemia study

The KMT2E (MLL5) gene encodes a histone methyltransferase implicated in the positive control of genes related to haematopoiesis. Its close relationship with retinoic acid-induced granulopoiesis suggests that the deregulated expression of KMT2E might lead acute promyelocytic leukaemia (APL) blasts to become less susceptible to the conventional treatment protocols. Here, we assessed the impact of KMT2E expression on the prognosis of 121 APL patients treated with ATRA and anthracycline-based chemotherapy. Univariate analysis showed that complete remission (P = 0·006), 2-year overall survival (OS) (P = 0·005) and 2-year disease-free survival (DFS) rates (P = 0·037) were significantly lower in patients with low KMT2E expression; additionally, the 2-year cumulative incidence of relapse was higher in patients with low KMT2E expression (P = 0·04). Multivariate analysis revealed that low KMT2E expression was independently associated with lower remission rate (odds ratio [OR]: 7·18, 95% confidence interval [CI]: 1·71-30·1; P = 0·007) and shorter OS (hazard ratio [HR]: 0·27, 95% CI: 0·08-0·87; P = 0·029). Evaluated as a continuous variable, KMT2E expression retained association with poor remission rate (OR: 10·3, 95% CI: 2·49-43·2; P = 0·001) and shorter survival (HR: 0·17, 95% IC: 0·05-0·53; P = 0·002), while the association with DFS was of marginal significance (HR: 1·01; 95% CI: 0·99-1·02; P = 0·06). In summary, low KMT2E expression may predict poor outcome in APL patients.

Treatment of acute promyelocytic leukemia with arsenic trioxide: clinical results and open questions

Acute promyelocytic leukemia (APL) is a rare form of acute myeloid leukemia. The specific translocation t(15;17), which results in the fusion gene PML-RARA is the diagnostic and pathomechanistic hallmark of APL. By combination, treatment consisting of the differentiating agent all-trans retinoic acid (ATRA), which targets this molecular lesion, and cytotoxic chemotherapy, cure can be achieved in over 70% of patients. Recently, arsenic trioxide (ATO) has emerged to be the most active single agent in the treatment of APL. Previous studies employing ATO in relapse settings reported average complete remission rates of 85% and a mean overall survival of over 60%. In recent approaches installing ATO in first-line treatment, ATO-induced response rates comparable to previous combination regimen. The results of these newer studies indicate that the backbone of chemotherapy can be dramatically reduced or completely replaced by ATO and ATRA with similar or even better outcome.

Arsenic trioxide in front-line therapy of acute promyelocytic leukemia (C9710): prognostic significance of FLT3 mutations and complex karyotype

The addition of arsenic trioxide (ATO) to frontline therapy of acute promyelocytic leukemia (APL) has been shown to result in significant improvements in disease-free survival (DFS). FLT3 mutations are frequently observed in APL, but its prognostic significance remains unclear. We analyzed 245 newly diagnosed adult patients with APL treated on intergroup trial C9710 and evaluated previously defined biological and prognostic factors and their relationship to FLT3 mutations and to additional karyotypic abnormalities. FLT3 mutations were found in 48% of patients, including 31% with an internal tandem duplication (FLT3-ITD), 14% with a point mutation (FLT3-D835) and 2% with both mutations. The FLT3-ITD mutant level was uniformly low, < 0.5. Neither FLT3 mutation had an impact on remission rate, induction death rate, DFS or overall survival (OS). The addition of ATO consolidation improved outcomes regardless of FLT3 mutation type or level, initial white blood cell count, PML-RARA isoform type or transcript level. The presence of a complex karyotype was strongly associated with an inferior OS independently of post-remission treatment. In conclusion, the addition of ATO to frontline therapy overcomes the impact of previously described adverse prognostic factors including FLT3 mutations. However, complex karyotype is strongly associated with an inferior OS despite ATO therapy.

Analysis of class I and II aberrations in Iraqi childhood acute myeloid leukemia using filter paper cards

The lack of molecular diagnosis in the field of cancer in Iraq has motivated us to perform a genetic analysis of pediatric acute myelogenous leukemia (AML), including class I and II aberrations. Peripheral blood or bone marrow cells were collected from 134 AML children aged ≤15 years. Flinders Technology Associates (FTA) filter paper cards were used to transfer dried blood samples from five Iraqi hospitals to Japan. DNA sequencing was performed to identify class I mutations. Nested RT-PCR was used to detect class II aberrations, except that MLL rearrangement was detected according to long distance inverse-PCR. NPM1 and FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) mutations were analyzed by GeneScan using DNA template. Among 134 Iraqi pediatric AML samples, the most prevalent FAB subtype was M2 (33.6 %) followed by M3 (17.9 %). Class I mutations: 20 (14.9 %), 8 (6.0 %), and 8 (6.0 %) patients had FLT3-ITD, FLT3-TKD, and KIT mutations, respectively. Class II mutations: 24 (17.9 %), 19 (14.2 %), and 9 (6.7 %) children had PML-RARA, RUNX1-RUNX1T1, and CBFB-MYH11 transcripts, respectively. MLL rearrangements were detected in 25 (18.7 %) patients. NPM1 mutation was detected in seven (5.2 %) cases. Collectively, approximately 30 % of AML children were proved to carry favorable prognostic genetic abnormalities, whereas approximately 10 % had high FLT3-ITD allelic burden and needed a special treatment plan including allogeneic hematopoietic stem cell transplantation. Acute promyelocytic leukemia (APL) was frequent among Iraqi pediatric AML. It is likely that molecular diagnosis using FTA cards in underdeveloped countries could guide doctors towards an appropriate treatment strategy.

One acute promyelocytic leukemia patient underwent complete molecular remission with consistent presence of t (2; 3) (p25; q21) karyotype

OBJECTIVES

This study aimed to explore why one acute promyelocytic leukemia (APL) patient underwent complete molecular remission in the persistent presence of the t (2; 3) (p25; q21) karotype.

METHODS

One APL patient overexpressed PML/RARα (bcr1) and WT1 genes in the presence of the Fms-like tyrosine kinase-internal tandem duplication mutation, while cytogenetics showed t (2; 3) (p25; q21) and t (15; 17) (q22; q21). Cytogenetics and molecular biology were monitored throughout the treatment.

RESULTS

After 5 weeks of induction chemotherapy, this case gained complete molecular biology remission with the presence of t (2; 3) (p25; q21). This status was still present during the follow-up consolidate and maintenance therapy.

CONCLUSION

For this patient, t (2; 3) (p25; q21) may be one kind of balanced translocation that leads to miscarriages or causes abnormalities in children, unrelated to leukemia or other malignancies.

The Impact of FLT3 Mutations on the Development of Acute Myeloid Leukemias

The development of the genetic studies on acute myeloid leukemias (AMLs) has led to the identification of some recurrent genetic abnormalities. Their discovery was of fundamental importance not only for a better understanding of the molecular pathogenesis of AMLs, but also for the identification of new therapeutic targets. In this context, it is essential to identify AML-associated “driver” mutations, which have a causative role in leukemogenesis. Evidences accumulated during the last years indicate that activating internal tandem duplication mutations in FLT3 (FLT3-ITD), detected in about 20% of AMLs, represents driver mutations and valid therapeutic targets in AMLs. Furthermore, the screening of FLT3-ITD mutations has also considerably helped to improve the identification of more accurate prognostic criteria and of the therapeutic selection of patients.

Management of elderly patients with acute promyelocytic leukemia: progress and problems

Despite substantial progress in the management and outcome of acute promyelocytic leukemia (APL) during the last decades, older age remains a prominent negative prognostic factor. The improvement of long-term stabilization and cure of older APL patients is therefore a particular challenge. Data of unselected population-based studies suggest a high rate of exclusion from clinical trials in older age. The comparison of registry and study data indicates that study patients represent a positive selection. Older APL patients seem as sensitive to therapy as younger patients. With conventional therapy, based on all-trans retinoic acid (ATRA) and chemotherapy, over 50 % of older APL patients can probably be cured. Special problems of advanced age are the high rate of early death before or during induction therapy and the high frequency of death in remission with negative influence on the outcome. Both may be related in part to a higher vulnerability against the common treatment with ATRA and chemotherapy. Alternative less toxic approaches including arsenic trioxide (ATO) with or without ATRA and combinations with gemtuzumab ozogamicin or with reduced chemotherapy can induce long-lasting remission in all stages of APL. Considering the high curative potential and the excellent tolerance of ATO in newly diagnosed and relapsed APL, older patients are probably a particular target group for a chemotherapy-free approach with ATO.

DNA methylation changes are a late event in acute promyelocytic leukemia and coincide with loss of transcription factor binding

The origin of aberrant DNA methylation in cancer remains largely unknown. In the present study, we elucidated the DNA methylome in primary acute promyelocytic leukemia (APL) and the role of promyelocytic leukemia–retinoic acid receptor α (PML-RARα) in establishing these patterns. Cells from APL patients showed increased genome-wide DNA methylation with higher variability than healthy CD34+ cells, promyelocytes, and remission BM cells. A core set of differentially methylated regions in APL was identified. Age at diagnosis, Sanz score, and Flt3-mutation status characterized methylation subtypes. Transcription factor–binding sites (eg, the c-myc–binding sites) were associated with low methylation. However, SUZ12- and REST-binding sites identified in embryonic stem cells were preferentially DNA hypermethylated in APL cells. Unexpectedly, PML-RARα–binding sites were also protected from aberrant DNA methylation in APL cells. Consistent with this, myeloid cells from preleukemic PML-RARα knock-in mice did not show altered DNA methylation and the expression of PML-RARα in hematopoietic progenitor cells prevented differentiation without affecting DNA methylation. Treatment of APL blasts with all-trans retinoic acid also did not result in immediate DNA methylation changes. The results of the present study suggest that aberrant DNA methylation is associated with leukemia phenotype but is not required for PML-RARα–mediated initiation of leukemogenesis.

Acute promyelocytic leukemia with Flt3-TKD and WT1 mutations relapsing in a testicle and followed by systemic relapse

Extramedullary relapse is a rare phenomenon in patients with acute promyelocytic leukemia (APL), especially that derived from urogenital systems like the testicles. In this report, we describe an APL patient who had received standard induction/maintenance therapy resulting in durable remission for 4.5 years, when he presented with a unilateral testicular mass confirmed as myeloid sarcoma; this was followed by systemic relapse of APL. Retrospective analysis of the involved blood and bone marrow samples at the time of the initial diagnosis revealed a rare point mutation of FLT3-TKD and a novel mutation of WT1. These mutations were detected recurrently throughout the course of the disease. After reinduction therapy with arsenic trioxide and all-trans retinoic acid combined with daunorubicin, complete hematological remission was achieved for the ensuing salvage allogeneic hematopoietic stem cell transplant.

Early Death in Two Patients with Acute Promyelocytic Leukemia Presenting the bcr3 Isoform, FLT3-ITD Mutation, and Elevated WT1 Level

Despite major advances in the treatment of acute promyelocytic leukemia (APL), the problem of early death (ED) remains unsolved. Alongside the currently known clinical and hematological risk factors, prognostic significance has been attributed to internal tandem duplication mutations of the fms-like tyrosine kinase-3 (FLT3-ITD), hypogranular variant morphology, and the bcr-3 isoform of PML-RARα. We describe premature death of two patients with the hypogranular variant of APL who presented remarkably high expression levels of Wilms' tumor gene (WT1). Our results point to WT1 as an important prognostic factor of ED that needs to be promptly evaluated in all newly diagnosed cases of APL.

Treatment-influenced associations of PML-RARα mutations, FLT3 mutations, and additional chromosome abnormalities in relapsed acute promyelocytic leukemia

Mutations in the all-trans retinoic acid (ATRA)-targeted ligand binding domain of PML-RARα (PRα/LBD+) have been implicated in the passive selection of ATRA-resistant acute promyelocytic leukemia clones leading to disease relapse. Among 45 relapse patients from the ATRA/chemotherapy arm of intergroup protocol C9710, 18 patients harbored PRα/LBD+ (40%), 7 of whom (39%) relapsed Off-ATRA selection pressure, suggesting a possible active role of PRα/LBD+. Of 41 relapse patients coanalyzed, 15 (37%) had FMS-related tyrosine kinase 3 internal tandem duplication mutations (FLT3-ITD+), which were differentially associated with PRα/LBD+ depending on ATRA treatment status at relapse: positively, On-ATRA; negatively, Off-ATRA. Thirteen of 21 patients (62%) had additional chromosome abnormalities (ACAs); all coanalyzed PRα/LBD mutant patients who relapsed off-ATRA (n = 5) had associated ACA. After relapse Off-ATRA, ACA and FLT3-ITD+ were negatively associated and were oppositely associated with presenting white blood count and PML-RARα type: ACA, low, L-isoform; FLT3-ITD+, high, S-isoform. These exploratory results suggest that differing PRα/LBD+ activities may interact with FLT3-ITD+ or ACA, that FLT3-ITD+ and ACA are associated with different intrinsic disease progression pathways manifest at relapse Off-ATRA, and that these different pathways may be short-circuited by ATRA-selectable defects at relapse On-ATRA. ACA and certain PRα/LBD+ were also associated with reduced postrelapse survival.

Diversity of the juxtamembrane and TKD1 mutations (exons 13-15) in the FLT3 gene with regards to mutant load, sequence, length, localization, and correlation with biological data

In acute myeloid leukemia (AML) mutations in the juxtamembrane and tyrosine kinase 1 domain (exons 13-15) of the FLT3 gene (FLT3-ITD/LM) are heterogeneous with respect to mutation load, size, and localization. We characterized length and structure of these mutations by fragment analysis and sequencing in 689 AML which were identified among 3,365 (20.5%) newly diagnosed AML (1,803 males, 1,562 females; 15.8-91.8 years). Mutations were heterogeneous in length (median: 63, range: 3-1,236 nucleotides; nt). Most frequent were sizes of 21 (8.4%) or 24 nt (6.0%). Ninety-one different insertion sites were observed (between nt 1,788 and 1,934, according to accession "FLT3 [Ensembl/Havana merge: ENSG00000122025]" with nt 1,856 (n = 41) and 1,863 (n = 35) being most frequent. In addition, 89 different insertion end points were observed between nt 1,790 and 1,994. FLT3-mutation/wild-type ratio was available in 615 patients (median, 0.80; range 0.03-181.73). 128 Patients (20.8%) had ratios <0.3, 334 (54.3%) had ratio ≥0.3 <1, 118 (19.2%) ≥1, and 35 (5.7%) showed complete loss of the FLT3-wild-type allele. Overall (OS) and event-free (EFS) survival were better for FLT3-negative than FLT3mut normal karyotype patients (P = 0.078 and P = 0.004, respectively) and patients with low level FLT3-mutations had significantly longer OS and EFS compared with high level mutations (FLT3-mutation/wild-type ratio ≥1) (P < 0.001 and P = 0.002, respectively). The length of the mutation had no prognostic impact. Mutations localized more 5' were associated with better outcome than more 3'mutations, but no strict association to certain functional domains was detected. In conclusion, FLT3-mutations are extremely heterogenous with mutation load being the most relevant parameter.