A randomized phase I clinical and biologic study of two schedules of sorafenib in patients with myelodysplastic syndrome or acute myeloid leukemia: a NCIC (National Cancer Institute of Canada) Clinical Trials Group Study

Phase 1 study of azacitidine in combination with quizartinib in patients with FLT3 or CBL mutated MDS and MDS/MPN

We conducted a phase 1 study evaluating 3 dose levels of quizartinib (30 mg, 40 mg or 60 mg) in combination with azacitidine for HMA-naïve or relapsed/refractory MDS or MDS/MPN with FLT3 or CBL mutations. Overall, 12 patients (HMA naïve: n=9, HMA failure: n=3) were enrolled; 7 (58 %) patients had FLT3 mutations and 5 (42 %) had CBL mutations. The maximum tolerated dose was not reached. Most common grade 3-4 treatment-emergent adverse events were thrombocytopenia (n=5, 42 %), anemia (n=4, 33 %), lung infection (n=2, 17 %), skin infection (n=2, 17 %), hyponatremia (n=2, 17 %) and sepsis (n=2, 17 %). The overall response rate was 83 % with median relapse-free and overall survivals of 15.1 months (95 % CI 0.0-38.4 months) and 17.5 months (95 % CI NC-NC), respectively. FLT3 mutation clearance was observed in 57 % (n=4) patients. These data suggest quizartinib is safe and shows encouraging activity in FLT3-mutated MDS and MDS/MPN. This study is registered at Clinicaltrials.gov as NCT04493138.

Efficacy analysis of different FLT3 inhibitors in patients with relapsed/refractory acute myeloid leukemia and high-risk myelodysplastic syndrome

Several FLT3 inhibitors(i) are available to treat relapsed/refractory (R/R) FLT3-internal tandem duplicated acute myeloid leukemia (AML). This study analyzes the efficacies of various FLT3i (types 1 and 2) tested in clinical trials in treating R/R AML and high-risk myelodysplastic syndromes (HR-MDS). PubMed and EMBASE databases were searched for single/double-arm phase I/II/III R/R AML or HR-MDS clinical trials published between 1/1/2000 and 6/1/2021. The outcomes studied were composite response rate (CRc) and overall response rate (ORR). Toxicities were compared based on the organ system. The 28 studies analyzed had 1927 patients. The pooled ORR and (CRc) for all FLT3i were 53% (95% CI, 43%-63%) and 34% (95% CI, 26%-44%). Pooled ORR and CRc were 37% (95% CI, 25%-51%) and 35% (95% CI, 21%-52%) for type 1 and 58% (95% CI, 43%-71%) and 38% (95% CI, 27%-50%) for type 2, respectively. Gastrointestinal (GI) and hematological toxicity occurred in 22% (95% CI, 19%-25.4%) and 74.6% (95% CI, 70%-79%) with type 1 and 13.9% (95% CI, 12%-16%) and 57.7% (95% CI, 54.6%-60.8%) with type 2 FLT3i. QTc prolongation occurred in 2.06% (95% CI, 1.03%-3.65%) with type 1 and 7% (95% CI, 5.3%-9%) with type 2 FLT3i. Type 2 FLT3i had less GI toxicity but more QTc prolongation. Prospective studies are needed to compare the efficacy of type 1 and 2 FLT3i.

A straightforward meta-analysis approach for oncology phase I dose-finding studies

Phase I early-phase clinical studies aim at investigating the safety and the underlying dose-toxicity relationship of a drug or combination. While little may still be known about the compound's properties, it is crucial to consider quantitative information available from any studies that may have been conducted previously on the same drug. A meta-analytic approach has the advantages of being able to properly account for between-study heterogeneity, and it may be readily extended to prediction or shrinkage applications. Here we propose a simple and robust two-stage approach for the estimation of maximum tolerated dose(s) utilizing penalized logistic regression and Bayesian random-effects meta-analysis methodology. Implementation is facilitated using standard R packages. The properties of the proposed methods are investigated in Monte Carlo simulations. The investigations are motivated and illustrated by two examples from oncology.

Borrowing historical information to improve phase I clinical trials using meta-analytic-predictive priors

Multiple phase I clinical trials may be performed to determine specific maximum tolerated doses (MTD) for specific races or cancer types. In these situations, borrowing historical information has potential to improve the accuracy of estimating toxicity rate and increase the probability of correctly targeting MTD. To utilize historical information in phase I clinical trials, we proposed using the Meta-Analytic-Predictive (MAP) priors to automatically estimate the heterogeneity between historical trials and give a relatively reasonable amount of borrowed information. We then applied MAP priors in some famous phase I trial designs, such as the continual reassessment method (CRM), Keyboard design and Bayesian optimal interval design (BOIN), to accomplish the process of dose finding. A clinical trial example and extended simulation studies show that our proposed methods have robust and efficient statistical performance, compared with those designs which do not consider borrowing information.

Acute myeloid leukemia with cup-like blasts and FLT3-ITD and NPM1 mutations mimics features of acute promyelocytic leukemia: a case of durable remission after sorafenib and low-dose cytarabine

Some previous researches raised the possibility of a novel acute myeloid leukemia (AML) entity presenting cup-like cytomorphology with mutations of both FLT3 and NPM1 or one of them. However, the clinical implications of this subtype remain unknown. We describe a 63-year-old patient belonging to this distinct AML subtype, who presented similar features of acute promyelocytic leukemia (APL) including nuclear morphology, negative for CD34 and HLA-DR, and abnormal coagulation. He had no response to both arsenic trioxide and CAG regimen (cytarabine, aclarubicin, and G-CSF). Given that the patient carried the FLT3-ITD mutation, we switched to a pilot treatment of FLT3 inhibitor sorafenib combined with low-dose cytarabine (LDAC). To date, the patient achieved durable complete remission over 58 months. These findings suggest that AML with cup-like blasts and FLT3-ITD and NPM1 mutations mimic APL, and the prognosis of this subtype may be improved by sorafenib combined with LDAC.

Leukoreductive response to the combination of sorafenib and chemotherapy in hyperleukocytosis of FLT3-ITD mutated pediatric AML

Twelve to 22% of pediatric acute myeloid leukemia (AML) patients present with hyperleukocytosis, which is one of the main risk factors of early death due to its clinical complications: leukostasis, causing pulmonary or central nervous system injuries, tumor lysis syndrome, and disseminated intravascular coagulation. Sorafenib is a multi-kinase inhibitor that blocks the Fms-Related Tyrosine Kinase 3 receptor (FLT3) in AML patients with a FLT3-internal tandem duplication (FLT3-ITD), leading to a reduction of proliferation. Here we report four de novo diagnosed or relapsed pediatric FLT3-ITD-positive AML patients with hyperleukocytosis, which were treated with sorafenib in combination with cytoreductive chemotherapy prior to the start of the induction phase. We observed a fast reduction of white blood cells in peripheral blood and bone marrow. This resulted in a rapid clinical stabilization of the patients. Adverse side effects-such as dermatologic toxicity, elevation of transaminases and hypertension-occurred but were mild and inductive chemotherapy could be started in parallel or subsequently. This implies sorafenib as a safe and effective treatment option in combination with chemotherapy during cytoreductive prephase for children with this life-threatening condition.

FMS-Like Tyrosine Kinase 3 Inhibitors for the Treatment of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia of adults, with a five-year survival that remains poor (approximately 25%). Knowledge and understanding of AML genomics have expanded tremendously over the past decade and are now included in AML prognostication and treatment decisions. FMS-like tyrosine kinase 3 (FLT3) is a Class III receptor tyrosine kinase (RTK) expressed primarily in the cell membranes of early hematopoietic progenitor cells, found in 28% of all patients with AML. FLT3 is the second most frequent mutation in adult AML following Nuclear-cytoplasmic shuttling phosphoprotein (NPM1), which is found in 50% of cases.¹ FLT3 inhibitors are promising new molecular therapeutics increasingly becoming standard of care for both newly diagnosed and relapsed/refractory FLT3 positive AML. This review will focus on the clinical trials/evidence, similarities, differences, clinical toxicities, and drug interactions relevant to treating clinicians as pertains to 5 FLT3-inhibitors: midostaurin, sorafenib, gilteritinib, crenolanib, and quizartinib.

Management of the Older Patient with Myelodysplastic Syndrome

No two diagnoses of myelodysplastic syndrome are genuinely alike, owing to differing and dynamic mutational topography and epigenetic aberrancy. Consequently, no two patients with myelodysplastic syndrome are identical and disease-specific and patient-specific factors are considered in formulating the optimal treatment, which includes few that are disease modifying. Age itself should not be an absolute contraindication to therapy, including intensive therapy such as allogeneic hematopoietic stem cell transplantation, which is the only curative therapy. However, age associates with an increased prevalence of frailty and comorbidities that must be considered and may preclude a path to cure. Palliative therapies are the mainstay for many patients with myelodysplastic syndrome, which is a disease of older adults with the majority of patients diagnosed at age ≥ 75 years. The older patient requires heightened attention to end organ function/reserve and drug-drug interactions as well as insurance, income, cost, and socioeconomic and psychosocial issues that influence management. Many prior studies have included relatively younger populations or have not specifically performed high-quality subgroup analyses of older patients. In this review, we discuss the available standard-of-care therapies for myelodysplastic syndrome as they specifically relate to the older population and assess the emerging therapeutics that may further the pursuit for personalized treatment and improve both the outcomes and quality of life of the older patient with myelodysplastic syndrome.

FLT3 Mutations in Acute Myeloid Leukemia: Key Concepts and Emerging Controversies

The FLT3 receptor is overexpressed on the majority of acute myeloid leukemia (AML) blasts. Mutations in FLT3 are the most common genetic alteration in AML, identified in approximately one third of newly diagnosed patients. FLT3 internal tandem duplication mutations (FLT3-ITD) are associated with increased relapse and inferior overall survival. Multiple small molecule inhibitors of FLT3 signaling have been identified, two of which (midostaurin and gilteritinib) are currently approved in the United States, and many more of which are in clinical trials. Despite significant advances, resistance to FLT3 inhibitors through secondary FLT3 mutations, upregulation of parallel pathways, and extracellular signaling remains an ongoing challenge. Novel therapeutic strategies to overcome resistance, including combining FLT3 inhibitors with other antileukemic agents, development of new FLT3 inhibitors, and FLT3-directed immunotherapy are in active clinical development. Multiple questions regarding FLT3-mutated AML remain. In this review, we highlight several of the current most intriguing controversies in the field including the role of FLT3 inhibitors in maintenance therapy, the role of hematopoietic cell transplantation in FLT3-mutated AML, use of FLT3 inhibitors in FLT3 wild-type disease, significance of non-canonical FLT3 mutations, and finally, emerging concerns regarding clonal evolution.

Pharmacological Inhibition of Oncogenic STAT3 and STAT5 Signaling in Hematopoietic Cancers

Signal Transducer and Activator of Transcription (STAT) 3 and 5 are important effectors of cellular transformation, and aberrant STAT3 and STAT5 signaling have been demonstrated in hematopoietic cancers. STAT3 and STAT5 are common targets for different tyrosine kinase oncogenes (TKOs). In addition, STAT3 and STAT5 proteins were shown to contain activating mutations in some rare but aggressive leukemias/lymphomas. Both proteins also contribute to drug resistance in hematopoietic malignancies and are now well recognized as major targets in cancer treatment. The development of inhibitors targeting STAT3 and STAT5 has been the subject of intense investigations during the last decade. This review summarizes the current knowledge of oncogenic STAT3 and STAT5 functions in hematopoietic cancers as well as advances in preclinical and clinical development of pharmacological inhibitors.

Effects of Sorafenib and Arsenic Trioxide on U937 and KG-1 Cell Lines: Apoptosis or Autophagy?

Objective

Acute myeloid leukemia (AML) is a clonal disorder of hemopoietic progenitor cells. The Raf serine/threonine (Ser/Thr) protein kinase isoforms including B-Raf and RAF1, are the upstream in the MAPK cascade that play essential functions in regulating cellular proliferation and survival. Activated autophagy-related genes have a dual role in both cell death and cell survival in cancer cells. The cytotoxic activities of arsenic trioxide (ATO) were widely assessed in many cancers. Sorafenib is known as a multikinase inhibitor which acts through suppression of Ser/Thr kinase Raf that was reported to have a key role in tumor cell signaling, proliferation, and angiogenesis. In this study, we examined the combination effect of ATO and sorafenib in AML cell lines.

Materials and Methods

In this experimental study, we studied in vitro effects of ATO and sorafenib on human leukemia cell lines. The effective concentrations of compounds were determined by MTT assay in both single and combination treatments. Apoptosis was evaluated by annexin-V FITC staining. Finally, mRNA levels of apoptotic and autophagy genes were evaluated using real-time polymerase chain reaction (PCR).

Results

Data demonstrated that sorafenib, ATO, and their combination significantly increase the number of apoptotic cells. We found that the combination of ATO and sorafenib significantly reduces the viability of U937 and KG-1 cells. The expression level of selective autophagy genes, ULK1 and Beclin1 decreased but LC3-II increased in U937.

Conclusion

The expression levels of apoptotic and autophagy activator genes were increased in response to treatment. The crosstalk between apoptosis and autophagy is a complicated mechanism and further investigations seem to be necessary.

Emerging treatment paradigms with FLT3 inhibitors in acute myeloid leukemia

Mutations in the fms-like tyrosine kinase 3 (FLT3) gene are detected in approximately one-third of patients with newly diagnosed acute myeloid leukemia (AML). These consist of the more common FLT3-internal tandem duplication (ITD) in approximately 20-25% of AML cases, and point mutations in the tyrosine kinase domain (TKD) in approximately 5-10%. FLT3 mutations, especially FLT3-ITD, are associated with proliferative disease, increased risk of relapse, and inferior overall survival when treated with conventional regimens. However, the recent development of well tolerated and active FLT3 inhibitors has significantly improved the outcomes of this aggressive subtype of AML. The multikinase inhibitor midostaurin was approved by the United States Food and Drug Administration (US FDA) in April 2017 for the frontline treatment of patients with FLT3-mutated (either ITD or TKD) AML in combination with induction chemotherapy, representing the first new drug approval in AML in nearly two decades. In November 2018, the US FDA also approved the second-generation FLT3 inhibitor gilteritinib as a single agent for patients with relapsed or refractory FLT3-mutated AML. Promising phase I and II efficacy data for quizartinib is likely to lead to a third regulatory approval in relapsed/refractory AML in the near future. However, despite the significant progress made in managing FLT3-mutated AML, many questions remain regarding the best approach to integrate these inhibitors into combination regimens, and also the optimal sequencing of different FLT3 inhibitors in various clinical settings. This review comprehensively examines the FLT3 inhibitors currently in clinical development, with an emphasis on their spectra of activity against different FLT3 mutations and other kinases, clinical safety and efficacy data, and their current and future roles in the management of AML. The mechanisms of resistance to FLT3 inhibitors and potential combination strategies to overcome such resistance pathways are also discussed.

Discontinuation of sorafenib can lead to the emergence of FLT3-ITD-positive acute myeloid leukemia

A 69-year-old woman who had been diagnosed with unresectable papillary thyroid cancer was referred to our hospital. We initially treated her with sorafenib, but she subsequently developed erythema multiforme, which was suspected to be a drug rush due to sorafenib; therefore, sorafenib was discontinued. At the time of discontinuation, immature blast cells were detected in her peripheral blood. Approximately two weeks later, her skin rash improved substantially, but the proportion of blasts in the peripheral blood increased. We performed a bone marrow examination, and she was diagnosed with FLT3-ITD-positive acute myeloid leukemia. FLT3-ITD expression is found in 20-25% of AML and is a known independent poor prognostic factor. To overcome the poor prognosis associated with FLT3-ITD, molecular drugs targeting FLT3-ITD are attracting much attention. Sorafenib, a multi-kinase inhibitor, also has an effect on FLT3-ITD. Although primary disease flares after tyrosine kinase inhibitor discontinuation have been reported, this is the first report to describe discontinuation of sorafenib treatment as a potential trigger of FLT3-ITD-positive acute myeloid leukemia in papillary thyroid cancer.

Use of FLT3 inhibitors in acute myeloid leukemia remission induction or salvage therapy: systematic review and meta-analysis

Background

Previous studies showed that FLT3 inhibitors played an important role in acute myeloid leukemia (AML) therapy. However, discrepancies remain regarding the association between FLT3 inhibitors use and prognosis of AML patients in clinical trials.

Aim

The aim of this study was to evaluate the effect of FLT3 inhibitors on the treatment of AML in a systematic review and meta-analysis.

Materials and methods

PubMed, Embase, and Cochrane Library databases were searched for studies published before August 2017 that used FLT3 inhibitors in AML. Fixed- and random-effect models were used, and between-study heterogeneity was assessed.

Results

A total of 26 studies fitting our inclusion and exclusion criteria were included. The FLT3 status of patients and main treatment outcomes including overall survival (OS), event-free survival (EFS), relapse-free survival (RFS), complete remission (CR), and overall response rate (ORR) after therapy were extracted. Five studies comparing addition of FLT3 inhibitors and placebo or blank control to chemotherapy were analyzed in Part I, showing improved OS (hazard ratio [HR]=0.86, 95% confidence interval [CI]=0.75–0.99, P=0.03) in the FLT3 inhibitor group but without a significant improvement on EFS (HR=0.86, 95% CI=0.62–1.21, P=0.39) and ORR (odds ratio [OR]=1.10, 95% CI=0.89–1.35, P=0.38). Twenty-one studies evaluating the benefit of using FLT3 inhibitors in different FLT3-type AML patients were analyzed in Part II, showing that FLT3–internal tandem duplication (ITD)-positive patients were more sensitive to FLT3 inhibitor treatment and achieved better CR (OR=1.89, 95% CI=1.06–3.37, P=0.03) and ORR (OR=3.07, 95% CI=2.13–4.43, P<0.001).

Conclusion

Our study showed that combined use of FLT3 inhibitors improved OS and that the FLT3 status of AML patients could affect their sensitivity to FLT3 inhibitors in terms of CR and ORR.

Protein Kinase Inhibitors as Therapeutic Drugs in AML: Advances and Challenges

Acute myeloid leukemia (AML) is a malignant blood disorder and the cure rate has been remarkably improved over the past decade. However, recurrent or refractory leu-kemia remains the major problem of the AML and no clearly effective therapy has been es-tablished so far. Traditional treatments such as chemotherapy and hematopoietic stem cell transplantation are both far dissatisfying the patients partly for their individual variety. Be-sides, conventional treatments usually have many side effects to result in poor prognosis. Therefore, an urgent need is necessary to update therapies of AML. To date, protein kinase inhibitors as new drugs offer hope for AML treatment and many of them are on clinical tri-als. Here, this review will provide a brief summary of protein kinase inhibitors investigated in AML thus far, mainly including tyrosine protein kinase inhibitors and serine/threonine kinase inhibitors. We also presented the sketch of signal pathways involving protein kinase inhibitors, as well as discussed the clinical applications and the challenges of inhibitors in AML treatment

Sorafenib Dose Recommendation in Acute Myeloid Leukemia Based on Exposure-FLT3 Relationship

Sorafenib administered at the approved dose continuously is not tolerated long-term in patients with acute myeloid leukemia (AML). The purpose of this study was to optimize the dosing regimen by characterizing the sorafenib exposure-response relationship in patients with AML. A one-compartment model with a transit absorption compartment and enterohepatic recirculation described the exposure. The relationship between sorafenib exposure and target modulation of kinase targets (FMS-like tyrosine kinase 3 (FLT3)-ITD and extracellular signal-regulated kinase (ERK)) were described by an inhibitory maximum effect (Emax ) model. Sorafenib could inhibit FLT3-ITD activity by 100% with an IC50 of 69.3 ng/mL and ERK activity by 84% with an IC50 of 85.7 ng/mL (both adjusted for metabolite potency). Different dosing regimens utilizing 200 or 400 mg at varying frequencies were simulated based on the exposure-response relationship. Simulations demonstrate that a 200 mg twice daily (b.i.d.) dosing regimen showed similar FLT3-ITD and ERK inhibitory activity compared with 400 mg b.i.d. and is recommended in further clinical trials in patients with AML.

Emerging therapies for acute myeloid leukemia: translating biology into the clinic

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with a poor outcome; overall survival is approximately 35% at two years and some subgroups have a less than 5% two-year survival. Recently, significant improvements have been made in our understanding of AML biology and genetics. These fundamental discoveries are now being translated into new therapies for this disease. This review will discuss recent advances in AML biology and the emerging treatments that are arising from biological studies. Specifically, we will consider new therapies that target molecular mutations in AML and dysregulated pathways such as apoptosis and mitochondrial metabolism. We will also discuss recent advances in immune and cellular therapy for AML.

Treatment of Relapsed/Refractory Acute Myeloid Leukemia

OPINION STATEMENT

Approximately 40-45% of younger and 10-20% of older adults with acute myeloid leukemia (AML) will be cured with current standard chemotherapy. The outlook is particularly gloomy for patients with relapsed and/or refractory disease (cure rates no higher than 10%). Allogeneic hematopoietic stem cell transplantation (HSCT), the only realistic hope of cure for these patients, is an option for only a minority. In recent years, much has been learned about the genomic and epigenomic landscapes of AML, and the clonal architecture of both de novo and secondary AML has begun to be unraveled. These advances have paved the way for rational drug development as new "drugable" targets have emerged. Although no new drug has been approved for AML in over four decades, with the exception of gemtuzumab ozogamycin, which was subsequently withdrawn, there is progress on the horizon with the possible regulatory approval soon of agents such as CPX-351 and midostaurin, the Food and Drug Administration "breakthrough" designation granted to venetoclax, and promising agents such as the IDH inhibitors AG-221 and AG-120, the smoothened inhibitor glasdegib and the histone deacetylase inhibitor pracinostat. In our practice, we treat most patients with relapsed/refractory AML on clinical trials, taking into consideration their prior treatment history and response to the same. We utilize targeted sequencing of genes frequently mutated in AML to identify "actionable" mutations, e.g., in FLT3 or IDH1/2, and incorporate small-molecule inhibitors of these oncogenic kinases into our therapeutic regimens whenever possible. In the absence of actionable mutations, we rationally combine conventional agents with other novel therapies such as monoclonal antibodies and other targeted drugs. For fit patients up to the age of 65, we often use high-dose cytarabine-containing backbone regimens. For older or unfit patients, we prefer hypomethylating agent-based therapy. Finally, all patients with relapsed/refractory AML are evaluated for allogeneic HSCT.

Anti-Vascular Endothelial Growth Factor Effects of Sorafenib and Arsenic Trioxide in Acute Myeloid Leukemia Cell Lines

Acute myeloid leukemia (AML), is a clonal disorder caused by acquired somatic mutations and chromosomal rearrangements. According to some evidence, progression of hematolymphoid malignancies depends on the induction of new blood vessel formation under the influence of acute leukemia. Various factors are produced by cancer cells under hypoxic conditions to increase vascular formation. Among these, vascular endothelial growth factor (VEGF) plays a crucial role. Cytotoxicity and anticancer effects of arsenic trioxide (ATO) have been reported in many cancers. Sorafenib, known as an angiogenic inhibitor, decreases leukemic cell survival. The aim of this study was to indicate combination effects of ATO and sorafenib in two AML cell lines, KG-1 and U937. Effective doses was determined by MTT assay for both single and combination treatments. Percentages of apoptotic cells were evaluated by Annexin V FITC staining and mRNA levels of VEGF isoforms and receptor expression were investigated by Real-Time PCR. Our data show that sorafenib (5μM and 7μM in KG-1 and U937 cell lines respectively), ATO (1.618μM and 1μM in KG-1 and U937 cell lines respectively), and also their combination significantly increased the percentage of apoptotic cells. In addition the mRNA level of VEGF isoforms was downregulated in the U937 cell line while upregulated in KG-1 cells. Taken together, our results suggest that the VEGF autocrine loop may have an influence on AML development and progression and could be consider as a therapeutic target. The combination of sorafenib as a VEGF inhibitor with ATO synergistically inhibits cell proliferation and promotes apoptosis.

Tyrosine kinase inhibitors targeting FLT3 in the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a cancer of the myeloid lineage of blood cells. Although significant progress has been made in treating many types of cancers during recent years, AML remains a deadly disease with survival rate lagging behind other blood cancers. A combination of toxic chemotherapies has been the standard AML treatment for more than 40 years. With intensive efforts to define the pathogenesis of AML, novel therapeutic drugs targeting key molecular defects in AML are being developed. Mutated in nearly 30% of AML, FMS-like tyrosine kinase 3 (FLT3) represents one of the most attractive targets. FLT3 mutants resulted from either internal tandem duplication (ITD) or point mutations possess enhanced kinase activity and cause constitutive activation of signaling. To date, several small molecule inhibitors of FLT3 have been developed but their clinical efficacy is limited due to a lack of potency and the generation of drug resistance. Therefore, next-generation FLT3 inhibitors overcoming these limitations are urgently in need. This review focuses on the pathological role of mutant FLT3 in the development of AML, the current status of FLT3 inhibitor development, and mechanisms underlining the development of resistance to existing FLT3 inhibitors.

[Sorafenib in combination with chemotherapy as first-line therapy for FLT3-ITD positive acute myeloid leukemia]

Objective: To analyze the clinical features of acute myeloid leukemia patients with Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutation and the therapeutic effect of sorafenib in combination with chemotherapy as first-line therapy for these patients. Methods: Clinical features and therapeutic effect were retrospectively analyzed in 53 AML patients with FLT3-ITD mutation diagnosed in Henan Cancer Hospital from January 2013 to August 2016. The biological characteristics and clinical efficacy of chemotherapy in combination with or without Sorafeinb were analyzed. Results: FLT3-ITD mutation was identified in 53 AML patients, 22 cases (41.5%) were M(5) subtype. The median of the peripheral WBC was 61.00 (0.98-920.00) ×10(9)/L, and there were 50 (94.3%) patients with WBC>10×10(9)/L. The median of blast cell in bone marrow was 0.730 (0.234-0.966) . The total remission rate of all these 53 patients was 56.6% (30/53) . The complete remission (CR) rates in patients treated with chemotherapy in combination with sorafenib and patients with chemotherapy alone were 86.4% (19/22) and 35.5% (11/31) , respectively. The 1-year overall survival rates of the two groups were 78.3%% and 50.0% (P=0.041) , and 1-year progression free survival rates were 75.9% and 42.4% (P=0.044) , respectively. Conclusion: AML patients with FLT3-ITD mutation have the characteristics of high peripheral WBC, high blast cells in bone marrow and accompanying with M(5) subtype. Sorafeinb combined with chemotherapy can significantly improve CR rate and short term survival.

Inefficiencies and Patient Burdens in the Development of the Targeted Cancer Drug Sorafenib: A Systematic Review

Failure in cancer drug development exacts heavy burdens on patients and research systems. To investigate inefficiencies and burdens in targeted drug development in cancer, we conducted a systematic review of all prelicensure trials for the anticancer drug, sorafenib (Bayer/Onyx Pharmaceuticals). We searched Embase and MEDLINE databases on October 14, 2014, for prelicensure clinical trials testing sorafenib against cancers. We measured risk by serious adverse event rates, benefit by objective response rates and survival, and trial success by prespecified primary endpoint attainment with acceptable toxicity. The first two clinically useful applications of sorafenib were discovered in the first 2 efficacy trials, after five drug-related deaths (4.6% of 108 total) and 93 total patient-years of involvement (2.4% of 3,928 total). Thereafter, sorafenib was tested in 26 indications and 67 drug combinations, leading to one additional licensure. Drug developers tested 5 indications in over 5 trials each, comprising 56 drug-related deaths (51.8% of 108 total) and 1,155 patient-years (29.4% of 3,928 total) of burden in unsuccessful attempts to discover utility against these malignancies. Overall, 32 Phase II trials (26% of Phase II activity) were duplicative, lacked appropriate follow-up, or were uninformative because of accrual failure, constituting 1,773 patients (15.6% of 11,355 total) participating in prelicensure sorafenib trials. The clinical utility of sorafenib was established early in development, with low burden on patients and resources. However, these early successes were followed by rapid and exhaustive testing against various malignancies and combination regimens, leading to excess patient burden. Our evaluation of sorafenib development suggests many opportunities for reducing costs and unnecessary patient burden in cancer drug development.

[Efficacy and safety of Sorafenib as monotherapy to FLT3-ITD positive acute myeloid leukemia]

Objective: To explore the efficacy and safety of Sorafenib as monotherapy to FLT3 positive acute myeloid leukemia (AML). Methods: From April 2014 to December 2015, fourteen AML patients with FLT3 positive, 7 males and 7 females with a median age of 42 (range: 14-81) years old, were enrolled in this study. Of the 14 cases, 4 were de novo cases, 9 refractory cases and 1 relapsed case, including 78.6% patients with severe complications and 57.1% patients with KPS score less than 60 [the median KPS score was 45 (20-70) ]. The administration of Sorafenib was 400 mg twice daily and Sorafenib was continued if tolerated. The treatment response was evaluated by MICM and the data were analyzed by paired samples t test before and after Sorafenib treatment. Results: The peripheral blood WBC count [4.2 (0.9-11.8) ×109/L vs 39.6 (2.3-209.5) ×109/L, P<0.001 ], the percentage of peripheral blast cell [0.07 (0-0.54) vs 0.53 (0-0.94), P<0.001] and the percentage of bone marrow blast cell [0.266 (0.020-0.880) vs 0.604 (0.180-0.900), P=0.003] were significantly decreased after Sorafenib monotherapy compared with before. The overall response rate was 57.1% (8/14), including 5 cases (35.7%) with complete remission (CR). Of 4 de novo cases, 2 achieved CR, 1 with PR, 1 with NR; 3 of 10 refractory and relapsed patients achieved CR and 2 cases achieved PR, 5 cases NR. The median duration of achieving molecular remission (FLT3-ITD negative) after Sorafenib was 46(33-72) days, and the median progression free survival (PFS) was 53 (28-175) days. Conclusion: Sorafenib shows activity in FLT3-ITD mutation positive AML patients. Sorafenib monotherapy could be used as a treatment option for elderly patients or patients with severe complications, and refractory and relapsed patients with not suitable for intensive chemotherapy.

'Acute myeloid leukemia: a comprehensive review and 2016 update'

Acute myeloid leukemia (AML) is the most common acute leukemia in adults, with an incidence of over 20 000 cases per year in the United States alone. Large chromosomal translocations as well as mutations in the genes involved in hematopoietic proliferation and differentiation result in the accumulation of poorly differentiated myeloid cells. AML is a highly heterogeneous disease; although cases can be stratified into favorable, intermediate and adverse-risk groups based on their cytogenetic profile, prognosis within these categories varies widely. The identification of recurrent genetic mutations, such as FLT3-ITD, NMP1 and CEBPA, has helped refine individual prognosis and guide management. Despite advances in supportive care, the backbone of therapy remains a combination of cytarabine- and anthracycline-based regimens with allogeneic stem cell transplantation for eligible candidates. Elderly patients are often unable to tolerate such regimens, and carry a particularly poor prognosis. Here, we review the major recent advances in the treatment of AML.

Acute myeloid leukemia: advancing clinical trials and promising therapeutics

Recent progress in understanding the biology of acute myeloid leukemia (AML) and the identification of targetable driver mutations, leukemia specific antigens and signal transduction pathways has ushered in a new era of therapy. In many circumstances the response rates with such targeted or antibody-based therapies are superior to those achieved with standard therapy and with decreased toxicity. In this review we discuss novel therapies in AML with a focus on two major areas of unmet need: (1) single agent and combination strategies to improve frontline therapy in elderly patients with AML and (2) molecularly targeted therapies in the frontline and salvage setting in all patients with AML.

Novel strategies to prevent relapse after allogeneic haematopoietic stem cell transplantation for acute myeloid leukaemia and myelodysplastic syndromes

PURPOSE OF REVIEW

Relapse of haematological neoplasms after allogeneic haematopoietic stem cell transplantation (HSCT) remains one of the leading causes of death. Treatment of relapse post-HSCT is frequently ineffective and outcomes are poor, necessitating preventive strategies that are reviewed below.

RECENT FINDINGS

Current strategies to prevent relapse after HSCT are geared towards four general principles: improving the antitumour effects of conditioning regimens prior to HSCT, improving graft selection and engineering to augment the graft-versus-leukaemia effect, post-HSCT chemotherapeutic interventions to impair growth of residual clonal cells and post-HSCT immune-mediated interventions to enhance the graft-versus-leukaemia effect. Strategies based on cell manipulation, namely natural killer (NK) cell enrichment and adoptive T cell transfer, are emerging. Targeted therapies including vaccinations, FLT3 inhibitors, mAbs and chimeric antigen receptor T cell therapy represent a new avenue of treating acute myeloid leukaemia (AML) and myelodysplastic syndromes (MDS). Studies are underway to incorporate all of these strategies in the clinical setting to determine their impact on relapse and survival after HSCT.

SUMMARY

The most recent evidence suggests that strategies using NK cell therapy and targeted immune therapies after HSCT may change the current landscape of HSCT for AML and MDS.

Novel agents for the treatment of childhood acute leukemia

Together, acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) make up approximately one-third of all pediatric cancer diagnoses. Despite remarkable improvement in the treatment outcomes of these diseases over the past several decades, the prognosis for certain high-risk groups of leukemia and for relapsed disease remains poor. However, recent insights into different types of 'driver' lesions of leukemogenesis, such as the aberrant activation of signaling pathways and various epigenetic modifications, have led to the discovery of novel agents that specifically target the mechanism of transformation. In parallel, emerging approaches in cancer immunotherapy have led to newer therapies that can exploit and harness cytotoxic immunity directed against malignant cells. This review details the rationale and implementation of recent and specifically targeted therapies in acute pediatric leukemia. Topics covered include the inhibition of critical cell signaling pathways [BCR-ABL, FMS-like tyrosine kinase 3 (FLT3), mammalian target of rapamycin (mTOR), and Janus-associated kinase (JAK)], proteasome inhibition, inhibition of epigenetic regulators of gene expression [DNA methyltransferase (DNMT) inhibitors, histone deacetylase (HDAC) inhibitors, and disruptor of telomeric signaling-1 (DOT1L) inhibitors], monoclonal antibodies and immunoconjugated toxins, bispecific T-cell engaging (BiTE) antibodies, and chimeric antigen receptor-modified (CAR) T cells.

Targeted Therapy of FLT3 in Treatment of AML-Current Status and Future Directions

Internal tandem duplications (ITDs) of the gene encoding the Fms-Like Tyrosine kinase-3 (FLT3) receptor are present in approximately 25% of patients with acute myeloid leukemia (AML). The mutation is associated with poor prognosis, and the aberrant protein product has been hypothesized as an attractive therapeutic target. Various tyrosine kinase inhibitors (TKIs) have been developed targeting FLT3, but in spite of initial optimism the first generation TKIs tested in clinical studies generally induce only partial and transient hematological responses. The limited treatment efficacy generally observed may be explained by numerous factors; extensively pretreated and high risk cohorts, suboptimal pharmacodynamic and pharmacokinetic properties of the compounds, acquired TKI resistance, or the possible fact that inhibition of mutated FLT3 alone is not sufficient to avoid disease progression. The second-generation agent quizartinb is showing promising outcomes and seems better tolerated and with less toxic effects than traditional chemotherapeutic agents. Therefore, new generations of TKIs might be feasible for use in combination therapy or in a salvage setting in selected patients. Here, we sum up experiences so far, and we discuss the future outlook of targeting dysregulated FLT3 signaling in the treatment of AML.

Mass cytometry: a highly multiplexed single-cell technology for advancing drug development

Advanced single-cell analysis technologies (e.g., mass cytometry) that help in multiplexing cellular measurements in limited-volume primary samples are critical in bridging discovery efforts to successful drug approval. Mass cytometry is the state-of-the-art technology in multiparametric single-cell analysis. Mass cytometers (also known as cytometry by time-of-flight or CyTOF) combine the cellular analysis principles of traditional fluorescence-based flow cytometry with the selectivity and quantitative power of inductively coupled plasma-mass spectrometry. Standard flow cytometry is limited in the number of parameters that can be measured owing to the overlap in signal when detecting fluorescently labeled antibodies. Mass cytometry uses antibodies tagged to stable isotopes of rare earth metals, which requires minimal signal compensation between the different metal tags. This unique feature enables researchers to seamlessly multiplex up to 40 independent measurements on single cells. In this overview we first present an overview of mass cytometry and compare it with traditional flow cytometry. We then discuss the emerging and potential applications of CyTOF technology in the pharmaceutical industry, including quantitative and qualitative deep profiling of immune cells and their applications in assessing drug immunogenicity, extensive mapping of signaling networks in single cells, cell surface receptor quantification and multiplexed internalization kinetics, multiplexing sample analysis by barcoding, and establishing cell ontologies on the basis of phenotype and/or function. We end with a discussion of the anticipated impact of this technology on drug development lifecycle with special emphasis on the utility of mass cytometry in deciphering a drug's pharmacokinetics and pharmacodynamics relationship.

The overexpression of KIT proto-oncogene in acute leukemic cells is not necessarily caused by the gene mutation

KIT is detected in a variety of cells, also in acute leukemia. Inhibition of wild-type KIT is not always satisfactory. The aim of this work was to evaluate the frequency of the most common KIT mutations in acute myeloid leukemia (AML) and determine the correlation between mutation and expression level. Samples were obtained from 75 patients with AL. CD117 presence was shown in 45 of 51 patients with AML and in 1 of 16 patients with acute lymphocytic leukemia (ALL). Asp816Val mutation was found in 3.5% of cases of AML and Val560Gly mutation in 1 sample with acute biclonal leukemia. Other genetic changes were found in 15 of 57 samples with AML: polymorphisms Met541Leu in 14% of cases, Lys546Lys in 7% and 1 case of acute biclonal leukemia, Ile798Ile in 5.3% of cases, Met541Leu in 1 acute biphenotypic leukemia and in 6.3% of ALL. Polymorphism Lys546Lys was also shown in 1 case of acute biclonal leukemia. Nonsilent genetic changes were detected in a total of 23% cases with core binding factor leukemia. There was no statistical significance between KIT expression and genetic changes. There was no correlation between the incidence and types of KIT mutations and its expression on cells in AML.

The Biology and Targeting of FLT3 in Pediatric Leukemia

Despite remarkable improvement in treatment outcomes in pediatric leukemia over the past several decades, the prognosis for high-risk groups of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), as well as for relapsed leukemia, remains poor. Intensification of chemotherapy regimens for those at highest risk has improved success rates, but at the cost of significantly increased morbidity and long-term adverse effects. With the success of imatinib in Philadelphia-chromosome-positive leukemia and all-trans retinoic acid in acute promyelocytic leukemia, the quest to find additional molecularly targeted therapies has generated much excitement over recent years. Another such possible target in pediatric acute leukemia is FMS-like tyrosine kinase 3 (FLT3). FLT3 aberrations are among the most frequently identified transforming events in AML, and have significant clinical implications in both high-risk pediatric AML and in certain high-risk groups of pediatric ALL. Therefore, the successful targeting of FLT3 has tremendous potential to improve outcomes in these subsets of patients. This article will give an overview of the molecular function and signaling of the FLT3 receptor, as well as its pathogenic role in leukemia. We review the discovery of targeting FLT3, discuss currently available FLT3 inhibitors in pediatric leukemia and results of clinical trials to date, and finally, consider the future promise and challenges of FLT3 inhibitor therapy.

Investigational FMS-like tyrosine kinase 3 inhibitors in treatment of acute myeloid leukemia

INTRODUCTION

Outcomes for the majority of patients with acute myeloid leukemia (AML) remain poor. Over the past decade, significant progress has been made in the understanding of the cytogenetic and molecular determinants of AML pathogenesis. One such advance is the identification of recurring mutations in the FMS-like tyrosine kinase 3 gene (FLT3). Currently, this marker, which appears in approximately one-third of all AML patients, not only signifies a poorer prognosis but also identifies an important target for therapy. FLT3 inhibitors have now undergone clinical evaluation in Phase I, II and III clinical trials, as both single agents and in combination with chemotherapeutics. Unfortunately, to date, none of the FLT3 inhibitors have gained FDA approval for the treatment of patients with AML. Yet, several promising FLT3 inhibitors are being evaluated in all phases of drug development.

AREAS COVERED

This review aims to highlight the agents furthest along in their development. It also focuses on those FLT3 inhibitors that are being evaluated in combination with other anti-leukemia agents.

EXPERT OPINION

The authors believe that the field of research for FLT3 inhibitors remains promising, despite the historically poor prognosis of this subgroup of patients with AML. The most promising areas of research will likely be the elucidation of the mechanisms of resistance to FLT3 inhibitors, and development of potent FLT3 inhibitors alone or in combination with hypomethylating agents, cytotoxic chemotherapy or with other targeted agents.

Sorafenib: targeting multiple tyrosine kinases in cancer

Sorafenib (BAY 43-9006, Nexavar®) is an oral multiple tyrosine kinase inhibitor. Main targets are receptor tyrosine kinase pathways frequently deregulated in cancer such as the Raf-Ras pathway, vascular endothelial growth factor (VEGF) pathway, and FMS-like tyrosine kinase 3 (FLT3). Sorafenib was approved by the FDA in fast track for advanced renal cell cancer and hepatocellular cancer and shows good clinical activity in thyroid cancer. Multiple clinical trials are undertaken to further investigate the role of sorafenib alone or in combination for the treatment of various tumor entities.

Sorafenib in Combination With Intensive Chemotherapy in Elderly Patients With Acute Myeloid Leukemia: Results From a Randomized, Placebo-Controlled Trial

Purpose

The prognosis of elderly patients with acute myeloid leukemia (AML) is still dismal even with intensive chemotherapy. In this trial, we compared the antileukemic activity of standard induction and consolidation therapy with or without the addition of the kinase inhibitor sorafenib in elderly patients with AML.

Patients and Methods

All patients received standard cytarabine and daunorubicin induction (7+3 regimen) and up to two cycles of intermediate-dose cytarabine consolidation. Two hundred one patients were equally randomly assigned to receive either sorafenib or placebo between the chemotherapy cycles and subsequently for up to 1 year after the beginning of therapy. The primary objective was to test for an improvement in event-free survival (EFS). Overall survival (OS), complete remission (CR) rate, tolerability, and several predefined subgroup analyses were among the secondary objectives.

Results

Age, sex, CR and early death (ED) probability, and prognostic factors were balanced between both study arms. Treatment in the sorafenib arm did not result in significant improvement in EFS or OS. This was also true for subgroup analyses, including the subgroup positive for FLT3 internal tandem duplications. Results of induction therapy were worse in the sorafenib arm, with higher treatment-related mortality and lower CR rates. More adverse effects occurred during induction therapy in the sorafenib arm, and patients in this arm received less consolidation chemotherapy as a result of higher induction toxicity.

Conclusion

In conclusion, combination of standard induction and consolidation therapy with sorafenib in the schedule investigated in our trial is not beneficial for elderly patients with AML.

The thorny issue of relapsed acute myeloid leukemia

PURPOSE OF REVIEW

Acute myeloid leukemia (AML) is a devastating disease, in which the majority of afflicted patients eventually experience relapse and die from their disease.

RECENT FINDINGS

Clinical and molecular characterization of the disease have greatly aided in prognostication in both primary and relapsed settings, which may broadly guide therapy, but truly effective standards of care for relapsed AML remain lacking. Traditional chemotherapeutic drugs have modest but limited efficacy in relapsed AML, whereas more novel and potent cytotoxic chemotherapeutic agents hold promise and are entering the advanced phases of testing. Targeted therapies for AML have demonstrated activity, often as single agents, generating enthusiasm for further development in subgroups of patients with appropriate molecular anomalies. Finally, allogeneic stem cell transplantation continues to evolve as an effective and potentially curative therapy for limited numbers of patients with relapsed AML.

SUMMARY

The complexity of relapsed AML will dictate the need for continued development of novel chemotherapeutic and targeted therapies that suit the molecular and clinical profiling of individual patients.

FLT3 inhibitors for acute myeloid leukemia: a review of their efficacy and mechanisms of resistance

Since the Food and Drug Administration approval of imatinib for treatment of chronic myeloid leukemia in 2001, tyrosine kinase inhibitors (TKIs) have become a mainstay in the care of many malignancies. In acute myeloid leukemia (AML), activating mutations in the FMS-like tyrosine kinase 3 (FLT3) gene result in survival and proliferation of leukemic blasts and are associated with adverse prognosis. Therefore, the FLT3 receptor is an appealing target for inhibition. Multiple small molecule TKIs are currently in development for FLT3-mutated AML, and agents are beginning to show promising efficacy. In other malignancies, the development of resistance to TKIs during the course of therapy has proven to be a challenge, and thus far, in clinical trials of FLT3 TKIs, resistance to inhibition represents a significant barrier to successful FLT3 inhibition. Understanding the mechanisms of resistance and overcoming these obstacles to target inhibition will be central to the success of these agents.

Salvage therapy for relapsed or refractory acute myeloid leukemia

There are a significant number of patients diagnosed with acute leukemia who either fail to achieve remission or who relapse thereafter. Challenges in treating this patient population include accurately assessing prognosis of disease and whether remission can be achieved; assessing the ability of patients to tolerate aggressive salvage therapies; choosing a salvage therapy that is most likely to succeed; and identifying suitable patients for hematopoietic stem cell transplantation. Despite the development of a variety of new investigational therapies, relapsed or refractory acute myeloid Leukemia remains a difficult clinical problem. Clinicians will need to consider all currently available approaches, including cytotoxic chemotherapy, targeted agents, and allogeneic stem cell transplantation, to optimize outcomes.

Quizartinib (AC220) is a potent second generation class III tyrosine kinase inhibitor that displays a distinct inhibition profile against mutant-FLT3, -PDGFRA and -KIT isoforms

Background

Activating mutations of class III receptor tyrosine kinases (RTK) FLT3, PDGFR and KIT are associated with multiple human neoplasms including hematologic malignancies, for example: systemic mast cell disorders (KIT), non-CML myeloproliferative neoplasms (PDGFR) and subsets of acute leukemias (FLT3 and KIT). First generation tyrosine kinase inhibitors (TKI) are rapidly being integrated into routine cancer care. However, the expanding spectrum of TK-mutations, bioavailability issues and the emerging problem of primary or secondary TKI-therapy resistance have lead to the search for novel second generation TKIs to improve target potency and to overcome resistant clones.

Quizartinib was recently demonstrated to be a selective FLT3 inhibitor with excellent pharmacokinetics and promising in vivo activity in a phase II study for FLT3 ITD + AML patients. In vitro kinase assays have suggested that in addition to FLT3, quizartinib also targets related class III RTK isoforms.

Methods

Various FLT3 or KIT leukemia cell lines and native blasts were used to determine the antiproliferative and proapoptotic efficacy of quizartinib. To better compare differences between the mutant kinase isoforms, we generated an isogenic BaF3 cell line expressing different FLT3, KIT or BCR/ABL isoforms. Using immunoblotting, we examined the effects of quizartinib on activation of mutant KIT or FLT3 isoforms.

Results

Kinase inhibition of (mutant) KIT, PDGFR and FLT3 isoforms by quizartinib leads to potent inhibition of cellular proliferation and induction of apoptosis in in vitro leukemia models as well as in native leukemia blasts treated ex vivo. However, the sensitivity patterns vary widely depending on the underlying (mutant)-kinase isoform, with some isoforms being relatively insensitive to this agent (e.g. FLT3 D835V and KIT codon D816 mutations). Evaluation of sensitivities in an isogenic cellular background confirms a direct association with the underlying mutant-TK isoform – which is further validated by immunoblotting experiments demonstrating kinase inhibition consistent with the cellular sensitivity/resistance to quizartinib.

Conclusion

Quizartinib is a potent second-generation class III receptor TK-inhibitor – but specific, mutation restricted spectrum of activity may require mutation screening prior to therapy.

Frequencies and prognostic impact of RAS mutations in MLL-rearranged acute lymphoblastic leukemia in infants

Acute lymphoblastic leukemia in infants represents an aggressive malignancy associated with a high incidence (approx. 80%) of translocations involving the Mixed Lineage Leukemia (MLL) gene. Attempts to mimic Mixed Lineage Leukemia fusion driven leukemogenesis in mice raised the question whether these fusion proteins require secondary hits. RAS mutations are suggested as candidates. Earlier results on the incidence of RAS mutations in Mixed Lineage Leukemia-rearranged acute lymphoblastic leukemia are inconclusive. Therefore, we studied frequencies and relation with clinical parameters of RAS mutations in a large cohort of infant acute lymphoblastic leukemia patients. Using conventional sequencing analysis, we screened neuroblastoma RAS viral (v-ras) oncogene homolog gene (NRAS), v-Ki-ras Kirsten rat sarcoma viral oncogene homolog gene (KRAS), and v-raf murine sarcoma viral oncogene homolog B1 gene (BRAF) for mutations in a large cohort (n=109) of infant acute lymphoblastic leukemia patients and studied the mutations in relation to several clinical parameters, and in relation to Homeobox gene A9 expression and the presence of ALL1 fused gene 4-Mixed Lineage Leukemia (AF4-MLL). Mutations were detected in approximately 14% of all cases, with a higher frequency of approximately 24% in t(4;11)-positive patients (P=0.04). Furthermore, we identified RAS mutations as an independent predictor (P=0.019) for poor outcome in Mixed Lineage Leukemia-rearranged infant acute lymphoblastic leukemia, with a hazard ratio of 3.194 (95% confidence interval (CI):1.211-8.429). Also, RAS-mutated infants have higher white blood cell counts at diagnosis (P=0.013), and are more resistant to glucocorticoids in vitro (P<0.05). Finally, we demonstrate that RAS mutations, and not the lack of Homeobox gene A9 expression nor the expression of AF4-MLL are associated with poor outcome in t(4;11)-rearranged infants. We conclude that the presence of RAS mutations in Mixed Lineage Leukemia-rearranged infant acute lymphoblastic leukemia is an independent predictor for a poor outcome. Therefore, future risk-stratification based on abnormal RAS-pathway activation and RAS-pathway inhibition could be beneficial in RAS-mutated infant acute lymphoblastic leukemia patients.