A case of FIP1L1-PDGFRA-positive chronic eosinophilic leukemia with a rare FIP1L1 breakpoint

Acute myeloid leukemia with a novel AKAP9::PDGFRA fusion transformed from essential thrombocythemia: A case report and mini review

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy associated with various combinations of gene mutations, epigenetic abnormalities, and chromosome rearrangement-related gene fusions. Despite the significant degree of heterogeneity in its pathogenesis, many gene fusions and point mutations are recurrent in AML and have been employed in risk stratification over the last several decades. Gene fusions have long been recognized for understanding tumorigenesis and their proven roles in clinical diagnosis and targeted therapies. Advances in DNA sequencing technologies and computational biology have contributed significantly to the detection of known fusion genes as well as for the discovery of novel ones. Several recurring gene fusions in AML have been linked to prognosis, treatment response, and disease progression. In this report, we present a case with a long history of essential thrombocythemia and hallmark CALR mutation transforming to AML characterized by a previously unreported AKAP9::PDGFRA fusion gene. We propose mechanisms by which this fusion may contribute to the pathogenesis of AML and its potential as a molecular target for tyrosine kinase inhibitors.

Eosinophilia characterized by a rare CCT6B mutation and responsive to tyrosine kinase inhibition: Case report and literature review

Hypereosinophilic syndrome is a rare disorder arising from neoplastic, or idiopathic causes. The availability of NGS panels has increasingly identified rare mutations as underlying pathogenic events and have led to reclassification of cases of idiopathic hypereosinophilic syndrome as chronic eosinophilic leukemia(CEL). In this report, we describe a case of a young man with hypereosinophilia whose disease initially did not fit the WHO criteria for CEL but harbored a rare mutation in CCT6B gene. We report our experience in successfully treating this patient with multiple tyrosine kinase inhibitors and provide literature review of this rare entity including potential treatment strategies.

Hypereosinophilic syndromes in the precision medicine era: clinical, molecular aspects and therapeutic approaches (targeted therapies)

Introduction: Hypereosinophilic syndromes are a heterogeneous group of disorders that may be associated with life-threatening organ injury as a result of tissues infiltration by eosinophils. The main goal of therapy is to mitigate eosinophil-mediated organ damage. When possible, therapy should be directed at the underlying etiology. However, even in the absence of any known cause, when organ damage is present, hypereosinophilia must be treated promptly and aggressively to reduce potential morbidity and mortality.Areas covered: Conventional therapies, including corticosteroids, hydroxyurea (hydroxycarbamide) and interferon-alpha, have shown variable efficacy and a non-negligible toxicity emphasizing the need of new therapeutic strategies based on drugs with different mechanisms of action.Expert opinion: Tyrosine kinase inhibitors have a central role among targeted therapies of hypereosinophilic syndromes. Imatinib, initially empirically used based on its activity in chronic myeloid leukemia, achieved preliminary excellent results further confirmed in large series of patients. Third-generation tyrosine kinase inhibitors such as ponatinib, while active in vitro and in vivo in animals, still deserve confirmation in properly designed clinical trials. In addition, clinical investigation on monoclonal antibodies against interleukin-5, interleukin-5Rα, IgE, and CD52 represents a promising area of research.

A complex and cryptic intrachromosomal rearrangement generating the FIP1L1_PDGFRA in adult acute myeloid leukemia

Myeloid neoplasms with eosinophilia and abnormalities of the PDGFRA gene can benefit from therapy with tyrosine kinase inhibitors, therefore revealing the PDGFRA rearrangement is essential to ensure the best choice of treatment. The most common PDGFRA partner is the FIP1L1 gene, generating the oncoprotein FIP1L1/PDGFRA (F/P). In the majority of cases the F/P fusion gene originates from intrachromosomal rearrangement at band 4q12, and occasionally from chromosomal translocations. In both cases, the interstitial chromosomal deletion of a region involving the CHIC2 gene has been reported, which is cryptic by conventional karyotyping but detectable by Fluorescence In Situ Hybridization (FISH) analyses. Herein, we report an acute myeloid leukemia (AML) case presenting with eosinophilia; the F/P fusion gene originated from a new, cryptic and complex intrachromosomal rearrangement of 4q12. Classical FISH assay revealed abnormal hybridization signals, but the presence of the F/P chimaeric gene was demonstrated by molecular analysis. We performed molecular characterization of the chromosomal rearrangement and targeted Next-Generation Sequencing (NGS) analysis with a myeloid gene panel, revealing the presence of pathogenic genomic variants affecting the TET2 and ETV6 genes. These mutations were present as subclones at the disease onset and their clone size increased at relapse.

Eosinophilia in acute myeloid leukemia: Overlooked and underexamined

The presence of eosinophilia in acute myeloid leukemia (AML) suggests an underlying core binding factor (CBF) lesion, a platelet derived growth factor (PDGFR) translocation, or another rare translocation (such as ETV6-ABL1). Each of these cytogenetic entities carries unique diagnostic, prognostic, and therapeutic implications. CBF AML is most common and as such, its treatment is more clearly established, consisting of intensive induction chemotherapy followed by cytarabine based consolidation. Due in large part to its intrinsic chemo-sensitivity, CBF AML is associated with relatively high rates of remission and survival. PDGFR mediated AML is comparatively rare, and as such, diagnostic and treatment paradigms are not as well defined. Early identification of PDGFR translocations is essential, as they confer profound imatinib sensitivity which may, in many instances, spare the need for chemotherapy. Prompt recognition of such lesions requires a strong index of suspicion, and as such these diagnoses are often initially overlooked. Unfortunately, many cases of PDGFR associated AML, particularly those with other concurrent cytogenetic abnormalities, demonstrate treatment emergent imatinib resistance. Such patients continue to present a challenge, even with the advent of novel tyrosine kinase inhibitors (TKIs). Patients with rare translocations such as ETV6-ABL1 are not well described however seem to follow an aggressive clinical course, with limited response to imatinib, and poor outcomes. This review examines the significance of eosinophilia in the context of AML, with respect to its presentation, pathology, and cytogenetics, and with special attention to appropriate evaluation and treatment.

Fusion genes: A promising tool combating against cancer

The driving roles of fusion genes during tumorigenesis have been recognized for decades, with efficacies demonstrated in clinical diagnosis and targeted therapy. With advances in sequencing technologies and computational biology, a surge in the identification of fusion genes has been witnessed during the past decade. The discovery and presence of splicing based fusions in normal tissues have challenged our canonical conceptions on fusion genes and offered us novel medical opportunities. The specificity of fusion genes to neoplastic tissues and their diverse functionalities during carcinogenesis foster them as promising tools in the battle against cancer. It is time to re-visit and comb through our cutting-edge knowledge on fusion genes to accelerate clinical translation of these internal markers. Urged as such, we are encouraged to categorize fusion events according to mechanisms leading to their generation, oncological consequences and clinical implications, offer insights on fusion occurrence across tumors from the system level, highlight feasible practices in fusion-related pharmaceutical development, and identify understudied yet important niches that may lead future research trend in this field.

Myeloid neoplasms with eosinophilia

Molecular diagnostics has generated substantial dividends in dissecting the genetic basis of myeloid neoplasms with eosinophilia. The family of diseases generated by dysregulated fusion tyrosine kinase (TK) genes is recognized by the World Health Organization (WHO) category, “Myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1, or with PCM1-JAK2.” In addition to myeloproliferative neoplasms (MPN), these patients can present with myelodysplastic syndrome/MPN, as well as de novo or secondary mixed-phenotype leukemias or lymphomas. Eosinophilia is a common, but not invariable, feature of these diseases. The natural history of PDGFRA- and PDGFRB-rearranged neoplasms has been dramatically altered by imatinib. In contrast, patients with FGFR1 and JAK2 fusion TK genes exhibit a more aggressive course and variable sensitivity to current TK inhibitors, and in most cases, long-term disease-free survival may only be achievable with allogeneic hematopoietic stem cell transplantation. Similar poor prognosis outcomes may be observed with rearrangements of FLT3 or ABL1 (eg, both of which commonly partner with ETV6), and further investigation is needed to validate their inclusion in the current WHO-defined group of eosinophilia-associated TK fusion-driven neoplasms. The diagnosis chronic eosinophilic leukemia, not otherwise specified (CEL, NOS) is assigned to patients with MPN with eosinophilia and nonspecific cytogenetic/molecular abnormalities and/or increased myeloblasts. Myeloid mutation panels have identified somatic variants in patients with a provisional diagnosis of hypereosinophilia of undetermined significance, reclassifying some of these cases as eosinophilia-associated neoplasms. Looking forward, one of the many challenges will be how to use the results of molecular profiling to guide prognosis and selection of actionable therapeutic targets.

Severe Prolonged Cough as Presenting Manifestation of FIP1L1-PDGFRA+ Chronic Eosinophilic Leukaemia: A Widely Ignored Association

Chronic eosinophilic leukaemia associated with the FIP1L1-PDGFRA fusion gene (F/P+ CEL) is a rare cause of marked persistent hypereosinophilia, arising almost exclusively in male patients. Clinical presentations are heterogeneous with a higher incidence of eosinophil-mediated cardiomyopathy than in other hypereosinophilic syndrome variants. Features of chronic myeloproliferative disease are often present, including splenomegaly and elevated serum vitamin B12 levels. The diagnosis is made by fluorescence in situ hybridization (FISH) showing the deletion of the CHIC2 locus and/or RT-PCR showing the FIP1L1-PDGFRA fusion transcript. Treatment with imatinib mesylate, a tyrosine kinase inhibitor, results in rapid and complete resolution of hypereosinophilia and associated symptoms, except for those related to sub-endocardial fibrosis that may be irreversible. We report the case of a male patient in whom isolated intractable cough remained the only clinical manifestation of F/P+ CEL for 4 years. Furthermore, eosinophil autofluorescence, an as yet unreported artefact in this setting, precluded the detection of the CHIC2 deletion and further delayed diagnosis, underlining that both FISH and RT-PCR should be performed when this disease is suspected.