The Impact of Flt3 Gene Mutations in Acute Promyelocytic Leukemia: A Meta-Analysis

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.

Risk factors and remaining challenges in the treatment of acute promyelocytic leukemia

The treatment of acute promyelocytic leukemia (APL) has evolved with the introduction of all-trans retinoic acid (ATRA) and subsequent arsenic trioxide (ATO), particularly in standard-risk APL with an initial white blood cell count (WBC) < 10,000/μL, where a high cure rate can now be achieved. However, for some patients with risk factors, early death or relapse remains a concern. Insights from the analysis of patients treated with ATRA and chemotherapy have identified risk factors such as WBC, surface antigens, complex karyotypes, FLT3 and other genetic mutations, p73 isoforms, variant rearrangements, and drug resistance mutations. However, in the ATRA + ATO era, the significance of these risk factors is changing. This article provides a comprehensive review of APL risk factors, taking into account the treatment approach, and explores the challenges associated with APL treatments.

Fatal intracranial haemorrhage in acute promyelocytic leukemia patients with short isoform of PML-RARα: Review of molecular and radiological data

Three major PML-RARα fusion gene transcripts (long [bcr1], variant [bcr2], and short [bcr3]) are currently used in clinical laboratories for the diagnosis and treatment monitoring of APL patients. Despite highly improved outcome, relapse and intracranial haemorrhage that may lead to early death is still an unsolved complication in APL. We reviewed APL patients confirmed by qPCR for the presence of PML-RARα transcripts (n = 27) and studied their outcome in relation to the isoform expression at diagnosis and follow-up in King Fahad Medical City. Eight in twenty-seven patients showed bcr3 and nineteen patients with bcr1 as major isoforms at diagnosis. Half of the bcr3 patients (n = 4/8) showed early mortality, prolonged qPCR positivity, 4-fold higher neutrophil/lymphocyte ratio, higher creatinine levels, and significantly reduced relapse free and overall survival time compared with bcr1 patients. Radiological findings in bcr3 patients revealed CNS involvement in the form of intracranial haemorrhage and periventricular microangiopathy and no CNS involvement in bcr1 patients. In conclusion, PML-RARα isoform expression at diagnosis in selective patients influences disease course over time and may even lead to early mortality due to haemorrhage. Thus, timely reporting of the specific PML-RARα isoform by clinical laboratories and CNS assessment by radiology can prevent complications leading to death in some APL patients.

Favorable outcome of PML-RARα short isoform and FLT3-ITD mutation in a patient with several adverse prognostic markers: A case report

Key Clinical Message

Complete molecular remission in a "variant APL" patient with short isoform of PML-RARα and FLT3-ITD mutation was achieved in response to ATRA and ATO plus IDA instead of standard treatment protocol. The use of FLT3 inhibitor in APL induction management is implicated to prevent differentiation syndrome and coagulopathy experienced in in patients with FLT3-ITD.

Abstract

FLT3-ITD mutations are the most common activating mutations in FLT3 gene, occurring in about 12 to 38% of acute promyelocytic leukemia cases, and are mainly associated with high white blood cell counts and poor clinical outcomes. Here, we present a case of APL variant with adverse prognostic features who showed short isoform [bcr3] of PML-RARα and FLT3-ITD mutation at diagnosis. The patient received all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) plus idarubicin (IDA) instead of standard treatment protocol, and achieved a complete morphological, cytogenetic and molecular response. However, the patient experienced differentiation syndrome, and coagulopathy that was subsequently resolved by continuous oxygen therapy, dexamethasone, and enoxaparin. The use of FLT3 inhibitor in APL induction management is implicated to prevent differentiation syndrome and coagulopathy in patients with FLT3-ITD mutation.

Acute Promyelocytic Leukemia with Rare Genetic Aberrations: A Report of Three Cases

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML) that is characterized by the PML::RARA fusion or, more rarely, a variant RARA translocation. While APL can be clinically suspected, diagnosis of APL requires genetic confirmation. Targeted therapy such as all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO) has dramatically improved the prognosis of APL patients, but this is dependent on timely genetic testing as different fusions and/or mutations can affect therapeutic outcomes. Here we report three APL cases with various genetic aberrations: cryptic PML::RARA fusion, variant RARA rearrangement, and typical PML::RARA fusion with co-existing FLT3-ITD mutation. They serve to illustrate the utility of integrating genetic testing, using chromosome analysis, fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR), and next-generation sequencing (NGS) in providing a detailed understanding of the genetic alterations underlying each patient's disease.

Association between FLT3-ITD and additional chromosomal abnormalities in the prognosis of acute promyelocytic leukemia

OBJECTIVES

Internal tandem duplications of the Fms-like tyrosine kinase 3 gene (FLT3-ITD) and additional chromosomal abnormalities (ACA) are prognostic factors in patients with acute promyelocytic leukemia (APL). This study aimed to determine the effect of the association between FLT3-ITD and ACA in the prognosis of APL.

METHODS

This was a retrospective cohort study including 60 patients with APL treated with all-trans retinoic acid (ATRA) and chemotherapy. Five-year overall survival (OS) and progression-free survival (PFS) were analyzed in patient groups according to the presence of FLT3-ITD and ACA.

RESULTS

FLT3-ITD was an independent adverse factor for 5-year PFS, and ACA was an independent adverse factor for 5-year OS. There were significant differences in OS and PFS among the groups: FLT3-ITD-negative without ACA, FLT3-ITD-positive without ACA, FLT3-ITD-negative with ACA, and FLT3-ITD-positive with ACA. The OS times were 52.917, 45.813, 25.375, and 23.417 months, and the PFS times were 48.833, 38.563, 23.250, and 17.333 months, respectively.

CONCLUSION

FLT3-ITD and ACA are associated with the poorest OS and PFS outcomes in patients with APL treated with chemotherapy plus ATRA.

Case Report: Successful therapy with all-trans retinoic acid combined with chemotherapy followed by hematopoietic stem cell transplantation for acute promyelocytic leukemia carrying the BCOR-RARA fusion gene

Acute promyelocytic leukemia (APL) is characterized by the balanced translocation of chromosomes 15 and 17, resulting in the formation of PML-RARA fusion gene. More than 98% of APL have PML-RARA fusion, and less than 2% have other types of RARA gene partners, which named variant APL (vAPL). In the present study, we reported a vAPL with BCOR-RARA, which was the third case of BCOR-RARA APL published. The patient achieved complete remission (CR) with all-trans retinoic acid (ATRA) monotherapy, and molecular CR with ATRA plus standard chemotherapy. After that, he underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) and ATRA maintenance and maintained a molecular CR status. This case provided valuable insights into the accurate identification of vAPL. Moreover, ATRA combined with chemotherapy followed by allo-HSCT was suggested as an optimal choice for those vAPL patients who had a high risk of relapse.

“FLipping” the Story: FLT3-Mutated Acute Myeloid Leukemia and the Evolving Role of FLT3 Inhibitors

Simple Summary

Patients with acute myeloid leukemia (AML) may have a number of different mutations. Those with mutations in the FLT3 gene have a higher risk of relapse and death than those lacking these mutations. FLT3 is a key receptor on the surface of AML cells, which drives cell survival and growth. Although activation of this receptor is normally tightly controlled, in AML, FLT3 mutations allow it to activate itself, independent of external control. Over the past 5 years, a number of new drugs have been developed to specifically target these mutations. In this article, we discuss these drugs and their uses, as well as the mechanisms by which AML cells may gain resistance to them and how that resistance can be overcome.

Abstract

The treatment of many types of cancers, including acute myeloid leukemia (AML), has been revolutionized by the development of therapeutics targeted at crucial molecular drivers of oncogenesis. In contrast to broad, relatively indiscriminate conventional chemotherapy, these targeted agents precisely disrupt key pathways within cancer cells. FMS-like tyrosine kinase 3 (FLT3)—encoding a critical regulator of hematopoiesis—is the most frequently mutated gene in patients with AML, and these mutations herald reduced survival and increased relapse in these patients. Approximately 30% of newly diagnosed AML carries an FLT3 mutation; of these, approximately three-quarters are internal tandem duplication (ITD) mutations, and the remainder are tyrosine kinase domain (TKD) mutations. In contrast to its usual, tightly controlled expression, FLT3-ITD mutants allow constitutive, “run-away” activation of a large number of key downstream pathways which promote cellular proliferation and survival. Targeted inhibition of FLT3 is, therefore, a promising therapeutic avenue. In April 2017, midostaurin became both the first FLT3 inhibitor and the first targeted therapy of any kind in AML to be approved by the US FDA. The use of FLT3 inhibitors has continued to grow as clinical trials continue to demonstrate the efficacy of this class of agents, with an expanding number available for use as both experimental standard-of-care usage. This review examines the biology of FLT3 and its downstream pathways, the mechanism of FLT3 inhibition, the development of the FLT3 inhibitors as a class and uses of the agents currently available clinically, and the mechanisms by which resistance to FLT3 inhibition may both develop and be overcome.

Acute Promyelocytic Leukemia Presenting With a Myeloid Sarcoma of the Spine: A Case Report and Literature Review

Myeloid sarcoma is a rare extramedullary tumor of immature myeloid cells. Certain known acute myeloid leukemia cytogenetic abnormalities, in particular t(8,21), has been associated with a higher incidence. Myeloid sarcoma, which rarely happens in acute promyelocytic leukemias, is more common in recurrent patients after the advent of all-trans retinoic acid (ATRA) and are rare in untreated acute promyelocytic leukemia. We described a case of, to our knowledge, de novo myeloid sarcoma of the spine confirmed as acute promyelocytic leukemia. Myeloid sarcoma is diagnosed by spinal tumor biopsy, and microscopic examination of a bone marrow smear and cytogenetic analysis led to a confirmed diagnosis of acute promyelocytic leukemia.

Optimal time-points for detecting expression levels of BAALC, EVI1, and WT1 genes in patients with acute myeloid leukemia: a meta-analysis

OBJECTIVES

This meta-analysis examined the prognostic role of brain and acute leukemia, cytoplasmic (BAALC), Ecotropic virus integration site-1 (EVI1) and Wilms' tumor 1 (WT1) genes at different time-points during conventional chemotherapy.

METHODS

A systematic search of publications indexed in the electronic databases from January 1988 to October 2020 was performed. Over 7525 cases of AML from 25 studies were involved.

RESULTS

At diagnosis, overexpression of either BAALC or EVI1 had a negative impact on complete remission achievement (Summary Odds ratios [SORs] for BAALC = 0.32; SORs for EVI1 = 0.49) and survival outcome. The summary hazard ratios of overall survival (OS) and disease-free survival (DFS) were 1.97 and 2.04 for BAALC and 1.33 and 1.86 for EVI1, respectively. The prognostic value of pretreatment WT1 levels was heterogeneous while subgroup analyses unveiled that overexpressed WT1 may correlate with a favorable outcome (summary hazard ratio [SHR] for OS = 0.42). Both WT1 and BAALC played a role in prognosis assessment at post-induction and the diagnostic performance of WT1 transcript reduction was superior to the absolute WT1 level. Post-consolidation WT1 overexpression consistently indicated an increased risk of relapse, while the combined HR for RFS was statistically insignificant (SHR = 4.22).

CONCLUSION

These findings confirm the application of BAALC and EVI1 at diagnosis, WT1 after induction chemotherapy in AML patients throughout conventional chemotherapy.

TERT genetic variability and telomere length as factors affecting survival and risk in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a neoplasm of immature myeloid cells characterized by various cytogenetic alterations. The present study showed that in addition to the FLT3-ITD and NPM1 mutation status, telomere length (TL) and telomerase reverse transcriptase (TERT) gene polymorphisms may affect risk and overall survival (OS) in AML. TL was longer in healthy controls than in AML patients and positively correlated with age in the patients, but not in healthy subjects. TL was found to be independently affected by the presence of the FLT3-ITD mutation. As for the TERT gene polymorphism, AML patients with the TERT rs2853669 CC genotype were characterized by significantly shorter OS than patients carrying the T allele. Another observation in our study is the difference in TL and OS in patients belonging to various risk stratification groups related to the FLT3-ITD and NPM1 mutation status. Patients with adverse risk classification (mutation in FLT3-ITD and lack of mutation in NPM1) presented with the shortest telomeres and significantly worse OS. In conclusion, OS of AML patients appears to be affected by TERT gene variability and TL in addition to other well-established factors such as age, WBC count, or FLT3-ITD and NPM1 mutation status.

Cytogenetics of Pediatric Acute Myeloid Leukemia: A Review of the Current Knowledge

Pediatric acute myeloid leukemia is a rare and heterogeneous disease in relation to morphology, immunophenotyping, germline and somatic cytogenetic and genetic abnormalities. Over recent decades, outcomes have greatly improved, although survival rates remain around 70% and the relapse rate is high, at around 30%. Cytogenetics is an important factor for diagnosis and indication of prognosis. The main cytogenetic abnormalities are referenced in the current WHO classification of acute myeloid leukemia, where there is an indication for risk-adapted therapy. The aim of this article is to provide an updated review of cytogenetics in pediatric AML, describing well-known WHO entities, as well as new subgroups and germline mutations with therapeutic implications. We describe the main chromosomal abnormalities, their frequency according to age and AML subtypes, and their prognostic relevance within current therapeutic protocols. We focus on de novo AML and on cytogenetic diagnosis, including the practical difficulties encountered, based on the most recent hematological and cytogenetic recommendations.

All-trans Retinoic Acid, Arsenic Trioxide, and Anthracycline-based Chemotherapy Improves Outcome in Newly Diagnosed Acute Promyelocytic Leukemia Regardless of FLT3-ITD Mutation Status

All-trans retinoic acid (ATRA) and pre-upfront arsenic trioxide (ATO) have revolutionized the therapy of acute promyelocytic leukemia (APL). However, internal tandem duplication of FMS-like tyrosine kinase 3 (FLT3-ITD) mutations is associated with increased risk of relapse. The aim of this study was to analyze the prognostic impact of FLT3-ITD on APL patients who received remission induction with ATRA, idarubicin (IDA) and/or ATO, followed by ATRA plus ATO along with anthracycline, as consolidation therapy. A total of 72 patients newly diagnosed with APL were included in this study. 83.3% of the patients achieved complete remission (CR) after induction therapy. FLT3-ITD mutations were detected in 16 (22.2%) patients and closely related to bcr-3 PML-RARa transcript (P<0.001). The 5-year overall survival (OS) rate was 100% in both FLT3-ITD^positive and FLT3-ITD^negative groups, and there was no significant difference in 5-year event-free survival (EFS) between the two groups (78.3% vs. 83.3%, P=0.85). ATRA plus ATO and anthracycline-based chemotherapy achieved great outcome in newly diagnosed APL regardless of the FLT3-ITD mutation status.

Gene mutations in acute promyelocytic leukemia early death in patients treated with arsenic trioxide alone

PURPOSE

APL patients have recurrent alterations in FLT3, WT1, NRAS and KRAS. Gene mutations have a strong potential for involvement in pathogenesis and may have potential effects on the clinical manifestations. Gene mutations may even be associated with early death (ED) in APL patients. However, there is little published information on mutations in APL patients and whether they are attributed to early death.

METHODS

In this study, we retrospectively analyzed the clinical data and gene mutations of 134 de novo APL patients. We detected the gene mutations by next-generation sequencing (NGS) to investigate the genetic predictors of early death in APL patients. According to the number of gene mutations per patient, the 134 APL patients were divided into three groups. All patients received arsenic trioxide (ATO) alone as induction therapy. The clinical data and gene mutations were compared and analyzed.

RESULTS

A total of 134 APL patients were involved in the study. The clinical data of sex, WBC, PT, and DD, UA, and LDH level were significantly different between the three groups (P = 0.000, P = 0.000, P = 0.009, P = 0.020, P = 0.030, P = 0.001 and P = 0.014, respectively). Meanwhile, among them, the Sanz risk stratification and early death rate were significantly different (P = 0.001). The early death rate was 10.4%, and the median time to early death was 6.6 days (range 2-15 days). For the next-generation sequencing, a mean of 1.28 ± 1.06 mutations per patient was detected (range: 0-5). The univariate and the multivariate regression analysis showed that age > 50[HR = 1.666, CI (1.027-2.702), P = 0.039], high WBC count [HR = 4.702, CI (1.026-21.543), P = 0.046] and low ALB levels [HR = 4.547, CI (1.088-18.995), P = 0.038] were independent risk factors for early death in APL patients. Furthermore, Kaplan-Meier survival analysis, univariate analysis, and the multivariate regression analysis showed that patients with multiple gene mutations [HR = 2.258, CI (1.115-4.571), P = 0.024], KRAS [HR = 5.136, CI (1.356-19.455), P = 0.016] and/or GATA2 [HR = 4.070, CI (1.287-12.877), P = 0.017] have a significantly higher early death rate.

CONCLUSION

The results of this investigation show that both molecular markers and clinical variables should be used as potential predictors for early death in APL patients. Our results suggested that age > 50, high WBC count, low ALB levels, and the presence of multiple gene mutations, KRAS and/or GATA2 at the time of diagnosis were independent risk factors for early death in APL patients. For these patients, clinicians should be more cautious during the course of induction treatment.

Cryptic t(15;17) acute promyelocytic leukemia with a karyotype of add(11)(p15) and t(13,20)- A case report with a literature review

Most acute promyelocytic leukemias (APL) are characterized by reciprocal translocations t(15;17)(q22;21), which results in the fusion of the promyelocytic leukemia protein (PML) gene at 15q22 with retinoic acid receptor a (RARα) gene at 17q21. However, several complex variant translocations also have been reported. Here, we report a 62-year-old man with typical morphology and clinical features of APL with a complex karyotype including add(11)(p15) and t(13;20)(q12;q11.2) without typical t(15;17) assayed by the G-banding analysis. The fluorescence in situ hybridization with a PML/RARα dual-color DNA probe showed an atypical fusion signal, quantitative real-time polymerase chain reaction analysis showed PML/RARα fusion transcripts, and NGS detected FLT3, WT1, and KRAS mutations. The patient achieved complete remission after treatment with conventional chemotherapy combined with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). Although the mechanism of this kind of cryptic variant remains unknown, we conclude that the cryptic PML/RARα fusion with add(11)(p15) and t(13;20)(q12;q11.2) seems not to alter the effectiveness of chemotherapy combined with ATRA and ATO.

Potential Effects of the FLT3-ITD Mutation on Chemotherapy Response and Prognosis of Acute Promyelocytic Leukemia

PURPOSE

To evaluate the influence of FLT3-ITD mutations on the treatment response and long-term survival of newly-diagnosed patients with acute promyelocytic leukemia (APL) treated with all-trans retinoic acid and arsenic trioxide.

METHODS

The long-term survival of 90 newly-diagnosed APL patients (age range 12-75 years) was retrospectively analyzed.The FLT3-ITD mutation rate was assayed by polymerase chain reaction (PCR) amplification and sequencing analysis. Its impact on the treatment response, event-free survival(EFS), or overall survival(OS) was investigated in patients with and without the mutations.

RESULTS

The FLT3-ITD mutation rate in newly-diagnosed APL patients was 20% (18/90). The white blood cell (WBC) count at diagnosis in patients with mutations was significantly higher than that in patients without mutations while the FLT3-ITD mutation rate was higher in the high-risk group than in the low/intermediate-risk group. Patients with mutations had a significantly higher early death (ED) rate (16.67% vs 1.39%) for those lacking the mutation (P =0.024). However, the complete remission (CR) and differentiation syndrome (DS) rates in the two groups were similar. Kaplan Meier analysis for EFS and OS at five years showed a significant difference between the patients stratified by FLT3-ITD mutation status (log-rank P =0.010 and P =0.009, respectively).

CONCLUSION

FLT3-ITD mutations can be related to high peripheral WBC counts in APL patients. APL patients with mutations displayed a higher ED rate compared to those without mutations. Patients carrying mutations had reduced five-year EFS and OS rates. Thus, reducing the overall death rate during induction treatment might be an effective way to improve the prognosis of patients with FLT3-ITD mutations.

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.

Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) cytogenetically characterized by a balanced reciprocal translocation between chromosomes 15 and 17, which results in the fusion between the promyelocytic leukemia (PML) gene and retinoic acid receptor-α (RARα) [...]

Nanopore sequencing sheds a light on the FLT3 gene mutations complexity in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) patients carry in 27% of cases an activating mutation of the fms-like tyrosine kinase-3 (FLT3) gene: internal tandem duplication (ITD) or tyrosine kinase domain (TKD) point mutation. The simultaneous presence of both types of mutations, so-called FLT3 dual mutations, has been reported in 2% of APL, but this circumstance has never been studied. We studied a cohort of 74 APL cases, performing an in-depth analysis of three FLT3 dual mutant cases. Nanopore sequencing (NS) allowed us to characterize their complex mutational profile, showing the occurrence of multiple activating FLT3 mutations on different alleles in the leukemic promyelocytes and suggesting a cumulative impact of these events on the constitutive activation of the FLT3 pathway in APL cells. NS approach not only sheds light on the FLT3 mutational complexity in APL, but may also be useful to better clarify the FLT3 mutations landscape in acute myeloid leukemia.

A novel variant of VEGFR2 identified by a pan-cancer screening of recurrent somatic mutations in the catalytic domain of tyrosine kinase receptors enhances tumor growth and metastasis

In cancer genomics, recurrence of mutations in gene families that share homologous domains has recently emerged as a reliable indicator of functional impact and can be exploited to reveal the pro-oncogenic effect of previously uncharacterized variants. Pan-cancer analyses of mutation hotspots in the catalytic domain of a subset of tyrosine kinase receptors revealed that two infrequent mutations of VEGFR2 (R1051Q and D1052N) recur in analogous proteins and correlate with reduced patient survival. Functional validation showed that both R1051Q and D1052N mutations increase the enzymatic activity of VEGFR2. The expression of VEGFR2^R1051Q potentiates the PI3K/Akt signaling axis in cancer cells, increasing their tumorigenic potential in vitro and in vivo. In addition, it confers to cancer cells an increased sensitivity to the VEGFR2-targeted tyrosine kinase inhibitor Linifanib. In the context of an efficacious application of anti-cancer targeted therapies, these findings indicate that the screening for uncharacterized mutations, like VEGFR2^R1051Q, may help to predict patient prognosis and drug response, with significant clinical implications.

Classic and Variants APLs, as Viewed from a Therapy Response

Most acute promyelocytic leukemia (APL) are caused by PML-RARA, a translocation-driven fusion oncoprotein discovered three decades ago. Over the years, several other types of rare X-RARA fusions have been described, while recently, oncogenic fusion proteins involving other retinoic acid receptors (RARB or RARG) have been associated to very rare cases of acute promyelocytic leukemia. PML-RARA driven pathogenesis and the molecular basis for therapy response have been the focus of many studies, which have now converged into an integrated physio-pathological model. The latter is well supported by clinical and molecular studies on patients, making APL one of the rare hematological disorder cured by targeted therapies. Here we review recent data on APL-like diseases not driven by the PML-RARA fusion and discuss these in view of current understanding of "classic" APL pathogenesis and therapy response.

Acute Promyelocytic Leukemia: A Constellation of Molecular Events around a Single PML-RARA Fusion Gene

Although acute promyelocytic leukemia (APL) is one of the most characterized forms of acute myeloid leukemia (AML), the molecular mechanisms involved in the development and progression of this disease are still a matter of study. APL is defined by the PML-RARA rearrangement as a consequence of the translocation t(15;17)(q24;q21). However, this abnormality alone is not able to trigger the whole leukemic phenotype and secondary cooperating events might contribute to APL pathogenesis. Additional somatic mutations are known to occur recurrently in several genes, such as FLT3, WT1, NRAS and KRAS, whereas mutations in other common AML genes are rarely detected, resulting in a different molecular profile compared to other AML subtypes. How this mutational spectrum, including point mutations in the PML-RARA fusion gene, could contribute to the 10%–15% of relapsed or resistant APL patients is still unknown. Moreover, due to the uncertain impact of additional mutations on prognosis, the identification of the APL-specific genetic lesion is still the only method recommended in the routine evaluation/screening at diagnosis and for minimal residual disease (MRD) assessment. However, the gene expression profile of genes, such as ID1, BAALC, ERG, and KMT2E, once combined with the molecular events, might improve future prognostic models, allowing us to predict clinical outcomes and to categorize APL patients in different risk subsets, as recently reported. In this review, we will focus on the molecular characterization of APL patients at diagnosis, relapse and resistance, in both children and adults. We will also describe different standardized molecular approaches to study MRD, including those recently developed. Finally, we will discuss how novel molecular findings can improve the management of this disease.

Advances in Pediatric Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) is a rare disease accounting for only 5%-10% of pediatric acute myeloid leukemia (AML) and fewer than 1000 cases occur annually in the United States across all age groups. Characterized by t (15; 17), with a resultant PML-RARA gene fusion driving leukemia development, advances in therapy have improved outcomes for APL significantly in the past several decades, now making APL the most curable form of AML in both children and adults. Cure rates in APL are now comparable to pediatric B-lymphoid leukemias. The success of APL treatment is due, in part, to the breadth of understanding of the driver PML-RARA mutation as well as collaborative efforts to quickly introduce and maximize the benefit of new therapies. Here, we review the presentation, clinical features, pathogenesis, and treatment advances in pediatric APL.