FIP1L1

Gene Summary

Gene:FIP1L1; factor interacting with PAPOLA and CPSF1
Aliases: Rhe, FIP1, hFip1
Location:4q12
Summary:This gene encodes a subunit of the CPSF (cleavage and polyadenylation specificity factor) complex that polyadenylates the 3' end of mRNA precursors. This gene, the homolog of yeast Fip1 (factor interacting with PAP), binds to U-rich sequences of pre-mRNA and stimulates poly(A) polymerase activity. Its N-terminus contains a PAP-binding site and its C-terminus an RNA-binding domain. An interstitial chromosomal deletion on 4q12 creates an in-frame fusion of human genes FIP1L1 and PDGFRA (platelet-derived growth factor receptor, alpha). The FIP1L1-PDGFRA fusion gene encodes a constitutively activated tyrosine kinase that joins the first 233 amino acids of FIP1L1 to the last 523 amino acids of PDGFRA. This gene fusion and chromosomal deletion is the cause of some forms of idiopathic hypereosinophilic syndrome (HES). This syndrome, recently reclassified as chronic eosinophilic leukemia (CEL), is responsive to treatment with tyrosine kinase inhibitors. Alternative splicing results in multiple transcript variants encoding distinct isoforms. [provided by RefSeq, Oct 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:pre-mRNA 3'-end-processing factor FIP1
Source:NCBIAccessed: 16 March, 2017

Ontology:

What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 16 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 16 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Entity Topic PubMed Papers
LeukaemiaFIP1L1-PDGFRA fusion in Leukemia
Fusions of the FIP1L1 and PDGFRA genes are reported in acute myeloid leukemia, T-cell lymphoblastic lymphoma, chronic eosinophilic leukemia - all with eosinophilia (Bain, 2010). Cools et al (2003) reported that many examples of what had previously been categorized as idiopathic hypereosinophilic syndrome were actually chronic eosinophilic leukemia - and that this condition with the FIP1L1-PDGFRA fusion is sensitive to treatments with tyrosine kinase inhibitors such as imatinib. Most FIP1L1-PDGFRA fusions are caused by a cryptic deletion: del(4)(q12), but occasionally by other rearrangements such as translocations t(1;4)(q44;q12)6 and t(4;10)(q12;p11).
View Publications72
-FIP1L1-PDGFRA Fusions in Myeloid Sarcoma
Myeloid sarcoma (aka granulocytic sarcoma) is a rare extramedullary tumor of immature granulocytic cells, usually accompanied by or following acute myeloid leukemia (Yilmaz et al, 2013). The fusion if the FIP1L1-PDGFRA genes is reported in some meyloid sarcomas.
View Publications7

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: FIP1L1 (cancer-related)

Appiah-Kubi K, Lan T, Wang Y, et al.
Platelet-derived growth factor receptors (PDGFRs) fusion genes involvement in hematological malignancies.
Crit Rev Oncol Hematol. 2017; 109:20-34 [PubMed] Related Publications
PURPOSE: To investigate oncogenic platelet-derived growth factor receptor(PDGFR) fusion genes involvement in hematological malignancies, the advances in the PDGFR fusion genes diagnosis and development of PDGFR fusions inhibitors.
METHODS: Literature search was done using terms "PDGFR and Fusion" or "PDGFR and Myeloid neoplasm" or 'PDGFR and Lymphoid neoplasm' or "PDGFR Fusion Diagnosis" or "PDGFR Fusion Targets" in databases including PubMed, ASCO.org, and Medscape.
RESULTS: Out of the 36 fusions detected, ETV6(TEL)-PDGFRB and FIP1L1-PDGFRA fusions were frequently detected, 33 are as a result of chromosomal translocation, FIP1L1-PDGFRA and EBF1-PDGFRB are the result of chromosomal deletion and CDK5RAP2- PDGFRΑ is the result of chromosomal insertion. Seven of the 34 rare fusions have detectable reciprocals.
CONCLUSION: RNA aptamers are promising therapeutic target of PDGFRs and diagnostic tools of PDGFRs fusion genes. Also, PDGFRs have variable prospective therapeutic strategies including small molecules, RNA aptamers, and interference therapeutics as well as development of adaptor protein Lnk mimetic drugs.

Maack A, Pegard A
Populus nigra (Salicaceae) absolute rich in phenolic acids, phenylpropanoïds and flavonoids as a new potent tyrosinase inhibitor.
Fitoterapia. 2016; 111:95-101 [PubMed] Related Publications
The purpose of this study was to evaluate the tyrosinase inhibitory capacity of Populus nigra buds absolute (PBA) and compare it to kojic acid (KA), controversial reference tyrosinase inhibitor. Populus nigra buds were extracted with hexane and ethanol to obtain PBA. The inhibitory effect of this absolute was first tested on the mushroom Agaricus bisporus tyrosinase. Then the depigmenting potential of PBA was tested on B16F10 murine melanocytes by assaying the activity of tyrosinase and melanin content. Consecutively, a microscopic analysis of intracellular melanin granules was performed. Finally, melanised reconstructed human epidermis (RHE) were used to assess the lightening potential activity of this PBA on human skin. Results show that PBA inhibits A. bisporus tyrosinase (IC50=77±8ppm) and inhibits melanocytes B16F10 tyrosinase (IC50=27±1ppm). PBA decreases intracellular melanin levels, with 50% loss at 39±9ppm. Finally, PBA at 1000ppm lightens RHE and decreases their melanin content of 20%. PBA is a strong inhibitor of tyrosinase and reduces melanogenesis in melanocytes B16F10. Thus, PBA has potential applications in skin-lightening cosmetics.

Roufosse F
Management of Hypereosinophilic Syndromes.
Immunol Allergy Clin North Am. 2015; 35(3):561-75 [PubMed] Related Publications
The symptomatic hypereosinophilic patient must be approached in a stepwise manner, with thorough assessment to determine whether the hypereosinophilia itself is contributing to damage and disease manifestations (thereby defining a hypereosinophilic syndrome), and to identify an eventual cause of hypereosinophilia, followed by initiation of treatment directed against the underlying condition or deleterious hypereosinophilic state. Situations encountered in the clinic are extremely heterogeneous because of the numerous potential causes of hypereosinophilia and the variable spectrum of eosinophil-mediated organ damage. A practical approach to many of these situations is presented in this review.

Zhou J, Papenhausen P, Shao H
Therapy-related acute myeloid leukemia with eosinophilia, basophilia, t(4;14)(q12;q24) and PDGFRA rearrangement: a case report and review of the literature.
Int J Clin Exp Pathol. 2015; 8(5):5812-20 [PubMed] Free Access to Full Article Related Publications
The myeloid and lymphoid neoplasms with eosinophilia and PDGFRA gene rearrangements usually show a good response to Imatinib and are typically associated with a normal karyotype, occasionally exhibiting a secondary chromosomal abnormality associated with clonal evolution. Five variant translocations involving PDGFRA have been reported. Here, we report a rare case of therapy-related acute myeloid leukemia with PDGFRA rearrangement after chemotherapy for prior B lymphoblastic leukemia (B-ALL). The patient had a history of BCR-ABL negative, hypodiploid B-ALL in complete remission after chemotherapy. However, 15 months later the patient developed acute myeloid leukemia with rapidly increasing eosinophilia, basophilia and a complex karyotype that included a novel t(4;14)(q12;q24). FIP1L1 was not associated with the PDGFRA rearrangement. The patient had a very aggressive clinical course, and died from the disease shortly after diagnosis. This is the first case of a primary therapy-related myeloid neoplasm with secondary PDGFRA rearrangement. The t(4:14)(q12;q24) is joining the growing list of the variant translocations involving PDGFRA.

Marton I, Pósfai É, Annus JK, et al.
WATERSHED INFARCTION IN HYPEREOSINOPHILIC SYNDROME: A DIAGNOSTIC DILEMMA IN FIP1L1-PDGFR ALPHA-ASSOCIATED MYELOID NEOPLASM.
Ideggyogy Sz. 2015; 68(5-6):212-6 [PubMed] Related Publications
INTRODUCTION: The FIP1L1-PDGFR alpha-positive, hypereosinophilic syndrome (HES) is a new category of hematological entities. Various clinical symptoms may occur, with no specific characteristics in either the clinical picture or the neuroimaging findings, and this may give rise to a diagnostic dilemma. A report on a long follow-up period (10 years) in a case of HES that presented with neuropsychiatric symptoms appears to be unique. Besides the complexity of the diagnostic process, the successful treatment is discussed.
CASE REPORT: The HES was diagnosed in a male patient at the age of 33 years, with involvement of the central nervous system and the myocardium. After the onset of the clinical signs, the MRI indicated bilateral cerebral and cerebellar cortico-subcortical lesions involving the watershed areas, mainly in the parieto-occipital regions. High-dose intravenous steroid (methylprednisolone 500 mg/day) alleviated the neurological symptoms within a few weeks, and the administration of imatinib (200 mg/day) resulted in an impressive regression of the hypereosinophilia and splenomegaly within 6 weeks. During the follow-up, the patient has continued to receive imatinib. The molecular remission has persisted, no new complaints have developed and the condition of the patient has remained stable.
CONCLUSION: The timely recognition of the HES and identification of the disease subtype which led to the administration of imatinib may be the key to successful treatment. The long stable follow-up period gives rise to a new dilemma in the treatment of the HES in these special cases: for how long should a patient receive a tyrosine kinase inhibitor, and may the treatment be suspended?

Schwaab J, Umbach R, Metzgeroth G, et al.
KIT D816V and JAK2 V617F mutations are seen recurrently in hypereosinophilia of unknown significance.
Am J Hematol. 2015; 90(9):774-7 [PubMed] Related Publications
Myeloproliferative neoplasms with eosinophilia are commonly characterized by a normal karyotype and remain poorly defined at the molecular level. We therefore investigated 426 samples from patients with hypereosinophilia of unknown significance initially referred for screening of the FIP1L1-PDGFRA (FP) fusion gene also for KIT D816V and JAK2 V617F mutations. Overall, 86 (20%) patients tested positive: FP+ in 55 (12%), KIT D816V+ in 14 (3%), and JAK2 V617F+ in 17 (4%) patients, respectively. To gain better insight into clinical characteristics, we compared these cases with 31 additional and well-characterized KIT D816V+ eosinophilia-associated systemic mastocytosis (SM-eo) patients enrolled within the "German Registry on Disorders of Eosinophils and Mast cells." Significant differences included younger age, male predominance, and higher eosinophil counts for FP+ cases while abdominal lymphadenopathy, ascites, and serum tryptase levels >100 μg/l were characteristic for those with KIT D816V. Leukocytes, hemoglobin, and splenomegaly did not differ significantly. A median of three additional mutations, most frequently TET2 and SRSF2, were identified in 12/13 KIT D816V+ SM-eo patients with available material indicating a more complex molecular pathogenesis. Median survival was not reached for FP+ cases but was only 26 and 41 months for KIT D816V+ SM and JAK2 V617F+ MPN-eo, respectively. Eosinophilia of ≥2 × 10(9) /l was identified as discriminator for inferior survival in KIT D816V+ and/or JAK2 V617F+ patients (median survival 20 months vs. not reached, P = 0.002). Thus, there is a clear prognostic and therapeutic rationale for detection of KIT D816V and JAK2 V617F in the diagnostic work up of eosinophilia.

Ziegler B, Peitsch WK, Reiter A, et al.
Generalized Eruptive Histiocytosis Associated With FIP1L1-PDGFRA-Positive Chronic Eosinophilic Leukemia.
JAMA Dermatol. 2015; 151(7):766-9 [PubMed] Related Publications
IMPORTANCE: Generalized eruptive histiocytosis (GEH) is a rare non-Langerhans cell histiocytosis with a benign, self-healing course. Neoplastic hematologic disorders of the myeloid lineage have been reported in association with GEH in 4 patients. A clonal association between GEH and the underlying leukemia was suspected in these patients but could only be confirmed in one patient.
OBSERVATIONS: A male patient in his 20s presented with asymptomatic red to brown macules and papules. A skin biopsy confirmed a diagnosis of GEH. His blood cell count revealed hypereosinophilia. Morphologic and molecular analyses from bone marrow and blood samples revealed FIP1L1-PDGFRA-positive chronic eosinophilic leukemia. The patient was treated with imatinib and achieved complete clinical remission of his leukemia and the GEH.
CONCLUSIONS AND RELEVANCE: To our knowledge, this is the first report of a patient with GEH associated with FIP1L1-PDGFRA-positive chronic eosinophilic leukemia. Generalized eruptive histiocytosis in association with a myeloid neoplasm may occur in 2 variants: a reactive condition or a clonal derivative of the underlying leukemia. In this case, both diseases responded well after initiation of treatment with imatinib.

Lekovic D, Bogdanovic A, Perunicic-Jovanovic M, et al.
Diagnostic challenges during pretreatment long-term follow-up in a patient with FIP1L1-PDGFRA-positive eosinophilia.
Intern Med. 2015; 54(6):637-42 [PubMed] Related Publications
Obtaining a precise characterization of eosinophilia is crucial, as successful treatment relies on the underlying etiology of the disease. Platelet-derived growth factor receptor alpha-related disorders were first specified in 2008 as a distinct group of clonal eosinophilic disorders with exceptional responsiveness to imatinib. We herein present the case of a man with myeloid neoplasm and eosinophilia in whom a definitive diagnosis could not be adequately made based on histopathological features who was ultimately diagnosed only after extensive molecular analyses and successfully treated with imatinib. In addition, we discuss the diagnostic and therapeutic approaches to treating patients presenting with eosinophilia.

Shen Y, Ren X, Ding K, et al.
Antitumor activity of S116836, a novel tyrosine kinase inhibitor, against imatinib-resistant FIP1L1-PDGFRα-expressing cells.
Oncotarget. 2014; 5(21):10407-20 [PubMed] Free Access to Full Article Related Publications
The FIP1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRα) fusion oncogene is the driver factor in a subset of patients with hypereosinophilic syndrome (HES)/chronic eosinophilic leukemia (CEL). Most FIP1L1-PDGFRα-positive patients respond well to the tyrosine kinase inhibitor (TKI) imatinib. Resistance to imatinib in HES/CEL has been described mainly due to the T674I mutation in FIP1L1-PDGFRα, which is homologous to the imatinib-resistant T315I mutation in BCR-ABL. Development of novel TKIs is imperative to overcome resistance to imatinib. We synthesized S116836, a novel TKI. In this study, we evaluated the antitumor activity of S116836 in FIP1L1-PDGFRα-expressing cells. The results showed that S116836 potently inhibited PDGFRα and its downstream signaling molecules such as STAT3, AKT, and Erk1/2. S116836 effectively inhibited the growth of the WT and T674I FIP1L1-PDGFRα-expressing neoplastic cells in vitro and in nude mouse xenografts. Moreover, S116836 induced intrinsic pathway of apoptosis as well as the death receptor pathway, coincided with up-regulation of the proapoptotic BH3-only protein Bim-EL through the Erk1/2 pathway. In conclusion, S116836 is active against WT and T674I FIP1L1-PDGFRα-expressing cells, and may be a prospective agent for the treatment of HES/CEL.

Kempf W, Kazakov DV, Szep Z, Vanecek T
CD30+ clonal T-cell lymphoid proliferation of the skin in a patient with hypereosinophilic syndrome.
J Cutan Pathol. 2015; 42(2):130-5 [PubMed] Related Publications
We report a hitherto undescribed unusual CD30+ clonal T-cell proliferation in a 46-year-old man with the lymphocytic variant of hypereosinophilic syndrome with a 17-year history of pruritus, generalized persistent papulonodular skin lesions and peripheral blood hypereosinophilia. A skin biopsy showed an eosinophil-rich infiltrate with small to medium-sized CD30+ lymphocytes and Churg-Strauss granulomas. Peripheral blood flow cytometry revealed an aberrant T-cell clone which, molecular genetically, was identical to the T-cell clone detected in the skin. No genetic aberrations of platelet-derived growth factor receptor alpha (PDGFRA), FIP1L1-PDGFRA, PDGFRB or FGFR1 were found. The skin lesions showed transient response to systemic and topical corticosteroids. The skin lesions represent cutaneous involvement by clonal T-cells in hypereosinophilic syndrome and differ from known cutaneous CD30+ lymphoproliferative disorders.

Jacobsen E, Pozdnyakova O, Redd R, et al.
Imatinib mesylate lacks efficacy in relapsed/refractory peripheral T cell lymphoma.
Leuk Lymphoma. 2015; 56(4):993-8 [PubMed] Related Publications
Platelet derived growth factor-α (PDGFR-α) is expressed in peripheral T cell lymphoma, not otherwise specified (PTCL, NOS). Imatinib mesylate demonstrated in vitro cytotoxicity against primary PTCL, NOS cells. We initiated a trial of imatinib in 12 patients with relapsed or refractory T-cell non-Hodgkin lymphoma (T-NHL). PDGFR-α expression by immunohistochemistry and fluorescence in situ hybridization (FISH) to assess for FIP1L1-PDGFR-α fusion and/or PDGFR-α amplification were not required for study entry. We documented no objective responses. The median progression-free survival was 21.0 days (90% confidence interval [CI] 15.0, 28.0) and median overall survival was 154 days (90% CI 35, 242). Four patients had tissue available for analysis of PDGFR-α by immunohistochemistry and three of these patients' tumors expressed PDGFR-α. Imatinib was not effective for the treatment of peripheral T cell lymphoma in an unselected group of patients in which PDGFR-α expression was not required for study entry.

Stojsic Z, Brasanac D, Stojanovic M, Boricic M
Cutaneous composite hemangioendothelioma: case report and review of published reports.
Ann Saudi Med. 2014 Mar-Apr; 34(2):182-8 [PubMed] Related Publications
Composite hemangioendothelioma (CHE) is a rare, locally aggressive, vascular tumor of intermediate-/ low-grade malignancy, and is characterized by varying combinations of benign, low-grade malignant, and malignant vascular components. In cutaneous localization, only 22 cases have been reported so far. A new case of CHE of the gluteal region in a 58-year-old man is described. Microscopically, vascular neoplasm, situated mainly within the deep dermis and the subcutaneous fat tissue, was composed of sinusoidal hemangioma, arteriovenous hemangioma, retiform hemangioendothelioma (RHE), and angiosarcoma. An average number of mitoses within the angiosarcomatous component was 10 per 10 high-power fields. Immunohistochemically, the tumor cells were positive for factor VIII-related antigen, CD34, and CD31 and negative for D2-40 and GLUT-1. Ki-67 labeling index was 21%, 1.2%, and 0% in the areas of angiosarcoma, RHE, and sinusoidal hemangioma, respectively. No recurrent disease was noted 3 months after the surgery. The present case displayed the following features previously undescribed in CHE: a novel component of sinusoidal hemangioma and localization at the gluteal region. We also provide review of clinical, histopathological, and immunohistochemical characteristics of cutaneous CHE from the published cases.

Iwasaki J, Kondo T, Darmanin S, et al.
FIP1L1 presence in FIP1L1-RARA or FIP1L1-PDGFRA differentially contributes to the pathogenesis of distinct types of leukemia.
Ann Hematol. 2014; 93(9):1473-81 [PubMed] Related Publications
FIP1-like 1 (FIP1L1) is associated with two leukemogenic fusion genes: FIP1L1-retinoic acid receptor alpha (RARA) and FIP1L1-platelet-derived growth factor receptor alpha (PDGFRA). Analyses of a series of deletion mutants revealed that the FIP1 motif in FIP1L1-RARA plays a pivotal role in its homodimerization and transcriptional repressor activity. However, in FIP1L1-PDGFRA, the C-terminal PDGFRA portion possesses the ability of forming a homodimer by itself, making FIP1L1 dispensable for constitutive activation of this kinase. Both the full-length and the C-terminal PDGFRA portion of FIP1L1-PDGFRA could transform the IL-3-dependent hematopoietic cell line, BAF-B03. Moreover, when either the full-length or the C-terminal PDGFRA portion of FIP1L1-PDGFRA was introduced in these cells, they grew in the absence of IL-3. The cells having the C-terminal PDGFRA portion of FIP1L1-PDGFRA, however, were partially IL-3 dependent, whereas the cells having the full-length FIP1L1-PDGFRA became completely IL-3 independent for their growth. Taken together, these results show that FIP1L1 differentially contributes to the pathogenesis of distinct types of leukemia.

Kovalszki A, Weller PF
Eosinophilia in mast cell disease.
Immunol Allergy Clin North Am. 2014; 34(2):357-64 [PubMed] Free Access to Full Article Related Publications
Eosinophils and mast cells coexist in clonal and nonclonal disorders. The interplay between these cells is complex and not fully understood. Discussed are both allergic/nonclonal disorders in which both cell types are increased in number are likely to play a role in pathogenesis and clonal disorders in which both cell types are affected and play key roles in pathogenesis. Finally, some treatment options, keeping both disorders in mind, are discussed. Future directions in thinking about these disorders are also briefly explored.

Shah S, Loghavi S, Garcia-Manero G, Khoury JD
Discovery of imatinib-responsive FIP1L1-PDGFRA mutation during refractory acute myeloid leukemia transformation of chronic myelomonocytic leukemia.
J Hematol Oncol. 2014; 7:26 [PubMed] Free Access to Full Article Related Publications
The FIP1L1-PDGFRA rearrangement results in constitutive activation of the tyrosine kinase PDGFRA. Neoplasms harboring this rearrangement are responsive to imatinib mesylate at doses much lower than those recommended for the treatment of chronic myelogenous leukemia. Only a single report has described the identification of FIP1L1-PDGFRA in chronic myelomonocytic leukemia (CMML). Herein, we present a case report of a patient in whom the FIP1L1-PDGFRA was discovered as he evolved from CMML to acute myeloid leukemia (AML). The presence of a dominant neoplastic clone with FIP1L1-PDGFRA rearrangement was suspected on the basis of sudden onset of peripheral and bone marrow eosinophilia and confirmed by fluorescence in situ hybridization and molecular diagnostic tests. Whereas the patient was initially refractory to chemotherapy before the rearrangement was detected, subsequent therapy with imatinib led to complete remission.

Noël LA, Arts FA, Montano-Almendras CP, et al.
The tyrosine phosphatase SHP2 is required for cell transformation by the receptor tyrosine kinase mutants FIP1L1-PDGFRα and PDGFRα D842V.
Mol Oncol. 2014; 8(3):728-40 [PubMed] Related Publications
Activated forms of the platelet derived growth factor receptor alpha (PDGFRα) have been described in various tumors, including FIP1L1-PDGFRα in patients with myeloproliferative diseases associated with hypereosinophilia and the PDGFRα(D842V) mutant in gastrointestinal stromal tumors and inflammatory fibroid polyps. To gain a better insight into the signal transduction mechanisms of PDGFRα oncogenes, we mutated twelve potentially phosphorylated tyrosine residues of FIP1L1-PDGFRα and identified three mutations that affected cell proliferation. In particular, mutation of tyrosine 720 in FIP1L1-PDGFRα or PDGFRα(D842V) inhibited cell growth and blocked ERK signaling in Ba/F3 cells. This mutation also decreased myeloproliferation in transplanted mice and the proliferation of human CD34(+) hematopoietic progenitors transduced with FIP1L1-PDGFRα. We showed that the non-receptor protein tyrosine phosphatase SHP2 bound directly to tyrosine 720 of FIP1L1-PDGFRα. SHP2 knock-down decreased proliferation of Ba/F3 cells transformed with FIP1L1-PDGFRα and PDGFRα(D842V) and affected ERK signaling, but not STAT5 phosphorylation. Remarkably, SHP2 was not essential for cell proliferation and ERK phosphorylation induced by the wild-type PDGF receptor in response to ligand stimulation, suggesting a shift in the function of SHP2 downstream of oncogenic receptors. In conclusion, our results indicate that SHP2 is required for cell transformation and ERK activation by mutant PDGF receptors.

Uchida T, Kitaura J, Nakahara F, et al.
Hes1 upregulation contributes to the development of FIP1L1-PDGRA-positive leukemia in blast crisis.
Exp Hematol. 2014; 42(5):369-379.e3 [PubMed] Related Publications
We have previously shown that elevated expression of Hairy enhancer of split 1 (Hes1) contributes to blast crisis transition in Bcr-Abl-positive chronic myelogenous leukemia. Here we investigate whether Hes1 is involved in the development of other myeloid neoplasms. Notably, Hes1 expression was elevated in only a few cases of 65 samples with different types of myeloid neoplasms. Interestingly, elevated expression of Hes1 was found in two of five samples of Fip1-like1 platelet-derived growth factor receptor-α (FIP1L1-PDGFA)-positive myeloid neoplasms associated with eosinophilia. Whereas FIP1L1-PDGFRα alone induced acute T-cell leukemia or myeloproliferative neoplasms in mouse bone marrow transplantation models, mice transplanted with bone marrow cells expressing both Hes1 and FIP1L1-PDGFRα developed acute leukemia characterized by an expansion of myeloid blasts and leukemic cells without eosinophilic granules. FIP1L1-PDGFRα conferred cytokine-independent growth to Hes1-transduced common myeloid progenitors, interleukin-3-dependent cells. Imatinib inhibited the growth of common myeloid progenitors expressing Hes1 with FIP1L1-PDGFRα, but not with imatinib-resistant FIP1L1-PDGFRα mutants harboring T674I or D842V. In contrast, ponatinib efficiently eradicated leukemic cells expressing Hes1 and the imatinib-resistant FLP1L1-PDGFRΑ mutant in vitro and in vivo. Thus, we have established mouse models of FIP1L1-PDGFRA-positive leukemia in myeloid blast crisis, which will help elucidate the pathogenesis of the disease and develop a new treatment for it.

Barraco D, Carobolante F, Candoni A, et al.
Complete and long-lasting cytologic and molecular remission of FIP1L1-PDGFRA-positive acute eosinophil myeloid leukaemia, treated with low-dose imatinib monotherapy.
Eur J Haematol. 2014; 92(6):541-5 [PubMed] Related Publications
Myeloproliferative neoplasms associated with FIP1L1-PDGFR rearrangements represent a rare subset of myeloid and lymphoid malignancies, characterised by the presence of eosinophilia and abnormalities of PDGFRA, PDGFRB or FGFR1 genes. The fusion product of such genes is a tyrosine kinase oncoprotein sensitive to imatinib, which to date results to be the standard of care for FIP1L1-PDGFRA-positive chronic myeloproliferative disorders with eosinophilia. However, the coexistence of FIP1L1-PDGFRA rearrangement associated with acute myeloid leukaemia is extremely rare. Here, we report a rare case of FIP1L1-PDGFRA-positive acute myeloid leukaemia, with marked peripheral blood and bone marrow eosinophilia, treated with low dose of imatinib monotherapy, achieving a rapid and long-lasting complete cytologic and molecular remission, without need for intensive chemotherapy.

Shen Y, Shi X, Pan J
The conformational control inhibitor of tyrosine kinases DCC-2036 is effective for imatinib-resistant cells expressing T674I FIP1L1-PDGFRα.
PLoS One. 2013; 8(8):e73059 [PubMed] Free Access to Full Article Related Publications
The cells expressing the T674I point mutant of FIP1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRα) in hypereosinophilics syndrome (HES) are resistant to imatinib and some second-generation tyrosine kinase inhibitors (TKIs). There is a desperate need to develop therapy to combat this acquired drug resistance. DCC-2036 has been synthesized as a third-generation TKI to combat especially the Bcr-Abl T315I mutant in chronic myeloid leukemia. This study evaluated the effect of DCC-2036 on FIP1L1-PDGFRα-positive cells, including the wild type (WT) and the T674I mutant. The in vitro effects of DCC-2036 on the PDGFRα signal pathways, proliferation, cell cycling and apoptosis of FIP1L1-PDGFRα-positive cells were investigated, and a nude mouse xenograft model was employed to assess the in vivo antitumor activity. We found that DCC-2036 decreased the phosphorylated levels of PDGFRα and its downstream targets without apparent effects on total protein levels. DCC-2036 inhibited proliferation, and induced apoptosis with MEK-dependent up-regulation of the pro-apoptotic protein Bim in FIP1L1-PDGFRα-positive cells. DCC-2036 also exhibited in vivo antineoplastic activity against cells with T674I FIP1L1-PDGFRα. In summary, FIP1L1-PDGFRα-positive cells are sensitive to DCC-2036 regardless of their sensitivity to imatinib. DCC-2036 may be a potential compound to treat imatinib-resistant HES.

Giacomini CP, Sun S, Varma S, et al.
Breakpoint analysis of transcriptional and genomic profiles uncovers novel gene fusions spanning multiple human cancer types.
PLoS Genet. 2013; 9(4):e1003464 [PubMed] Free Access to Full Article Related Publications
Gene fusions, like BCR/ABL1 in chronic myelogenous leukemia, have long been recognized in hematologic and mesenchymal malignancies. The recent finding of gene fusions in prostate and lung cancers has motivated the search for pathogenic gene fusions in other malignancies. Here, we developed a "breakpoint analysis" pipeline to discover candidate gene fusions by tell-tale transcript level or genomic DNA copy number transitions occurring within genes. Mining data from 974 diverse cancer samples, we identified 198 candidate fusions involving annotated cancer genes. From these, we validated and further characterized novel gene fusions involving ROS1 tyrosine kinase in angiosarcoma (CEP85L/ROS1), SLC1A2 glutamate transporter in colon cancer (APIP/SLC1A2), RAF1 kinase in pancreatic cancer (ATG7/RAF1) and anaplastic astrocytoma (BCL6/RAF1), EWSR1 in melanoma (EWSR1/CREM), CDK6 kinase in T-cell acute lymphoblastic leukemia (FAM133B/CDK6), and CLTC in breast cancer (CLTC/VMP1). Notably, while these fusions involved known cancer genes, all occurred with novel fusion partners and in previously unreported cancer types. Moreover, several constituted druggable targets (including kinases), with therapeutic implications for their respective malignancies. Lastly, breakpoint analysis identified new cell line models for known rearrangements, including EGFRvIII and FIP1L1/PDGFRA. Taken together, we provide a robust approach for gene fusion discovery, and our results highlight a more widespread role of fusion genes in cancer pathogenesis.

Montgomery ND, Dunphy CH, Mooberry M, et al.
Diagnostic complexities of eosinophilia.
Arch Pathol Lab Med. 2013; 137(2):259-69 [PubMed] Related Publications
CONTEXT: The advent of molecular tools capable of subclassifying eosinophilia has changed the diagnostic and clinical approach to what was classically called hypereosinophilic syndrome.
OBJECTIVES: To review the etiologies of eosinophilia and to describe the current diagnostic approach to this abnormality.
DATA SOURCES: Literature review.
CONCLUSION: Eosinophilia is a common, hematologic abnormality with diverse etiologies. The underlying causes can be broadly divided into reactive, clonal, and idiopathic. Classically, many cases of eosinophilia were grouped together into the umbrella category of hypereosinophilic syndrome, a clinical diagnosis of exclusion. In recent years, an improved mechanistic understanding of many eosinophilias has revolutionized the way these disorders are understood, diagnosed, and treated. As a result, specific diagnoses can now be assigned in many cases that were previously defined as hypereosinophilic syndrome. Most notably, chromosomal rearrangements, such as FIP1L1-PDGFRA fusions caused by internal deletions in chromosome 4, are now known to be associated with many chronic eosinophilic leukemias. When present, these specific molecular abnormalities predict response to directed therapies. Although an improved molecular understanding is revolutionizing the treatment of patients with rare causes of eosinophilia, it has also complicated the approach to evaluating and treating eosinophilia. Here, we review causes of eosinophilia and present a framework by which the practicing pathologist may approach this diagnostic dilemma. Finally, we consider recent cases as clinical examples of eosinophilia from a single institution, demonstrating the diversity of etiologies that must be considered.

Chen D, Bachanova V, Ketterling RP, et al.
A case of nonleukemic myeloid sarcoma with FIP1L1-PDGFRA rearrangement: an unusual presentation of a rare disease.
Am J Surg Pathol. 2013; 37(1):147-51 [PubMed] Related Publications
Rearrangement of the PDGFRA gene defines a distinct group of hematopoietic neoplasms that commonly present with persistent eosinophilia and are highly sensitive to low-dose imatinib mesylate treatment. Although rare cases of PDGFRA rearrangement-associated acute myeloid or lymphoblastic leukemia can occur, nonleukemic myeloid sarcoma has not been reported, and its sensitivity to imatinib treatment is unknown. Herein, we report a 31-year-old man with nonleukemic myeloid sarcoma and marked peripheral blood and bone marrow eosinophilia. Fluorescent in situ hybridization studies demonstrated that both bone marrow hematopoietic precursors and blasts of the myeloid sarcoma were positive for FIP1L1-PDGFRA rearrangement. The patient consequently received imatinib treatment at a dosage of 100 mg daily. After 3 weeks of therapy, his eosinophilia and myeloid sarcoma completely resolved, and at evaluation after 3 months he had attained bone marrow cytogenetic remission. To our knowledge, this is the first case of a nonleukemic myeloid sarcoma with the FIP1L1-PDGFRA rearrangement. Despite its aggressive clinical behavior attributed to myeloid sarcoma in general, the presence of PDGFRA rearrangement in this case conferred a high sensitivity to imatinib treatment and a favorable clinical outcome.

Paradies G, Zullino F, Orofino A, Leggio S
Rare extragonadal teratomas in children: complete tumor excision as a reliable and essential procedure for significant survival. Clinical experience and review of the literature.
Ann Ital Chir. 2014 Jan-Feb; 85(1):56-68 [PubMed] Related Publications
BACKGROUND: Extragonadal teratomas are rare tumors in neonates and infants and can sometimes show unusual, distinctive feature such as an unusual location, a clinical sometimes acute, presentation and a "fetiform" histotype of the lesion. We have extrapolated, from our entire experience of teratomas, 4 unusual cases, mostly operated as emergencies; 2 of them were treated just after birth. Aim of this paper is to report the clinical and pathological findings, to evaluate the surgical approach and the long-term biological behaviour in these cases, in the light of survival and current insights reported in the literature.
MATERIAL AND METHODS: The Authors reviewed the most significant (Tables I and II) clinical, laboratory, radiologic, and pathologic findings, surgical procedures, early and long-term results in 4 children, 1 male and 3 females (M/F ratio: 1/3), suffering from extragonadal teratomas, located in the temporo-zygomatic region of the head (Case n. 1, Fig. 1), retroperitoneal space (Case n. 2, Fig. 2) ,liver (Case n. 3, Figg. 3-5), kidney (Case n. 4, Fig. 6, 7), respectively. Of the 4 patients, 2 were treated neonatally (1 T. of the head, 1 retroperitoneal T.) A prenatal diagnosis had already been made in 2 of the 4 patients, between the 2nd and 3rd trimester of pregnancy, All the infants were born by scheduled caesarean section in a tertiary care hospital and were the immediately referred to thew N.I.C.Us. Because of a mostly acute clinical presentation, the 4 patients were then referred to the surgical unit at different ages: 7 days, 28 days, 7 months, and 4 years respectively. The initial clinical presentation (Table II) was consistent with the site of the mass and/or its side effects. The 2 newborns (Case 1 and 2) both with a prenatally diagnosed mass located at the temporozygomatic region and in the abdominal cavite respectively, already displayed, at birth a mass with a tendency to further growth. The symptoms and signs described to the primary care physician by the parents of the 2 patients suffering from intra-abdominal tumours (Cases n. 3, 4) were: swelling of the epigastrium and left hypochondrium due to a progressively growing hard mass, without impairment of the general, conditions in case n.3 (teratoma of the liver),while recurrent abdominal pain lasting for the 5 months was described in case n.4(retroperitoneal teratoma), followed by the development of an evident hard mass occupying the entire abdomen. In this case the symptoms suddenly worsened, with acute pain extending to the entire abdomen, high fever (>39° C), polypnea, anemia, deterioration of the general conditions and a rapid further enlargement of the mass. Antibiotic therapy was ansuccessful. The young child underwent a radiologic investigation (Fig. 6) that showed a large calcified mass in the left retroperitoneal space, associated with pleural effusion, In all the patients except for the Case n. 3, emergency surgical management was required and, in accordance with recommended practice, the procedure was complete exeresis.
RESULTS (TABLE I): All the 4 patients had an uneventful postoperative course. Clinical surveillance and tests of AFP and other markers were scheduled every 6 months for the first years and annually thereafter. At the current date they are alive, disease-free and have not suffered any recurrence with a follow-up as reported in Table I, of 7 years in case n. 2; 23 years in case n. 1; 42 years in case n. 3 and 36 years in case n. 4.
CONCLUSIONS: Some extragonadal teratomas of childhood of may rarely arise in the solid organs (liver, kidney), in the retroperitoneal space or the cranio-facial region, and also show unique histotype childhood characteristics ("fetiform") which distinguish them from more common cases. Being congenital tumours, prenatal diagnosis by US scan is extremely important in order to organize proper perinatal care in appropriate facilities where it is possible to define the diagnosis and carry out emergency surgery. An emergency procedure is frequently dictated both by complications related to the mass eddect and by the need to define the histology of the whole mass rather than just small biopsy specimens, Some teratomatas can hide more or less extensive islands of immaturity signs of malignant transformation that are clinically evident. It should be remembered that high serum levels of alpha-fetoprotein and calcficationof the imaging study, that are usually pathognomonic elements for fiagnosis, nay be lacking in abdominal lesions. Moreover, some additional specific diagnostic problems can be faced by either the radiologist (differential diagnosis from acquired or congenital cystic lesions, identification of the primary site of origin in the liver kidney or retroperitoneal space). Or the histopathologist (exclusion of renal metastasis of a primary gonadal teratomas of a glomerular and tubular differentiation a Wilm's tumour). The prognosis is generally benign, although the AIEOP guideline pointed out that high levels of circulating markers, including AFP, in children affected by mature or immature teratomas, could indicate rhe presence of micro-foci of YST, marking them out as at high risk. The UKCCSG II and the SFOP indicates AFP values exceeding 10,000 ng/ml as the threshold identifying a group of patients with a severe prognosis. The treatment indicated is early, complete exeresis, followed by a careful, exstensive, microscopic examination, associated, if necessary, with adjuvant chemotherapy. Finally, to improve the prognosis, close, long-term clinical, laboratory and imaging surveillance is necessary, at shorter intervals during the first 5 years after the exeresis and annually thereafter.

Santiago-Casiano M, Alemán JR, Matos-Fernández NA, et al.
No asthma, no parasites is a rare type of leukemia: chronic myeloid neoplasm with eosinophilia and abnormality of platelet-derived growth factor receptor alpha.
Bol Asoc Med P R. 2012 Jul-Sep; 104(3):41-6 [PubMed] Related Publications
Chronic myeloid neoplasm with eosinophilia and abnormality of platelet-derived growth factor receptor alpha (PDGFRA), referred as chronic eosinophilic leukemia, is an extremely rare neoplasm where long-term prognosis is uncertain though a high grade of responsiveness to Imatinib has been reported. The mortality and morbidity associated with chronic eosinophilic leukemia is associated with the degree of tissue involvement, damage, or both at diagnosis. We discuss a case of a young male patient with past medical history of hypoglycemia that presented to the emergency room with a complaints of a sharp abdominal pain localized in the upper quadrants. Laboratories were remarkable for elevated white blood cells with eosinophils predominance, anemia and thrombocytopenia. Bone marrow biopsy dislocated a FIP1L1-PDGFRA fusion gene chronic eosinophilic leukemia. Physicians need to have a high index of suspicion of this rare entity since not all eosinophilias can be interpreted as asthma or parasitis infections.

Alrwas A, Quesada JR, Marcos LA, et al.
Case of polycythemia vera concurrent with FIP1L1-PDGFRA-positive myeloproliferative neoplasm with eosinophilia.
Cancer Genet. 2012; 205(10):519-22 [PubMed] Related Publications
We report an unusual case of a symptomatic patient who initially had high hemoglobin and low serum erythropoietin levels, fitting a clinical diagnosis of polycythemia vera. However, after treatment with hydroxyurea and serial phlebotomies had been started, the patient developed hypereosinophilia, fitting the category of a myeloproliferative neoplasm with eosinophilia associated with the FIP1L1-PDGFRA gene fusion, as confirmed by molecular analysis. We discuss the clinical presentation, evolution, response to treatment, and pathogenetic implications of this case.

Lombardini ED, Summers BA
Two canine malignant vascular tumours with features of human retiform haemangioendothelioma.
J Comp Pathol. 2013; 148(2-3):225-9 [PubMed] Related Publications
Within the human medical literature, retiform haemangioendothelioma (RHE) is an established and well-recognized histopathological variant of endothelial tumours, but to date RHE has not been reported in animals. These tumours are characterized by the presence of elongate, arborizing vascular channels lined by neoplastic endothelium with prominent, often bulging ('hobnail') nuclei supported by a dense collagenous matrix and accompanied by abundant lymphoplasmacytic inflammation. Immunohistochemically, the neoplastic cells typically express endothelial markers such as von Willebrand factor and CD31. Human RHEs are categorized as low-grade malignancies. This report describes two canine vascular tumours with features consistent with RHE. In both cases there was suspected or known widespread tumour metastasis.

Tang TC, Chang H, Chuang WY
Complete response of myeloid sarcoma with FIP1L1-PDGFRA -associated myeloproliferative neoplasms to imatinib mesylate monotherapy.
Acta Haematol. 2012; 128(2):83-7 [PubMed] Related Publications
Myeloid sarcoma (MS) is a localized, extramedullary tumor of acute myeloid leukemia (AML) that typically presents either de novo or concomitantly with myeloproliferative neoplasms (MPN), AML and myelodysplastic syndrome. Patients who have MS must be treated with intensive chemotherapy, as are patients with AML, because MS usually progresses to a systemic manifestation and leads to dismal outcomes. FIP1L1-PDGFRA-associated MPN, a subtype of myeloid and lymphoid neoplasm, is characterized by eosinophilia and abnormalities in the PDGFRA, PDGFRB or FGFR1 gene. Fusion of the FIP1L1 and PDGFRA genes activates the tyrosine kinase. As a result, imatinib mesylate (IM) is widely used for the treatment of this disorder. The coexistence of FIP1L1-PDGFRA-associated MPN and MS is extremely rare. Patients with this condition fail to achieve durable remission and long-term survival without a combination of intensive chemotherapy and IM. Here, we report a case of MS and FIP1L1-PDGFRA-associated MPN that was successfully treated with IM monotherapy.

Gotlib J, Akin C
Mast cells and eosinophils in mastocytosis, chronic eosinophilic leukemia, and non-clonal disorders.
Semin Hematol. 2012; 49(2):128-37 [PubMed] Related Publications
Mast cells and eosinophils often travel in the same biologic circles. In non-clonal states, such as allergic and inflammatory conditions, cell-to-cell contact and the pleiotropic actions of multiple cytokines and chemokines, derived from local tissues or mast cells themselves, foster the co-recruitment of these cells to the same geographic cellular niche. While eosinophils and mast cells serve critical roles as part of the host immune response and in maintenance of normal homeostasis, these cell types can undergo neoplastic transformation due to the development of clonal molecular abnormalities that arise in early hematopoietic progenitors. The dysregulated tyrosine kinases, D816V KIT and FIP1L1-PDGFRA, are the prototypic oncogenic lesions resulting in systemic mastocytosis (SM) and chronic eosinophilic leukemia, respectively. We review the pathobiology of these myeloproliferative neoplasms (MPNs) with a focus on the relationship between mast cells and eosinophils, and discuss murine models, which further elucidate how the phenotype of these diseases can be influenced by stem cell factor (SCF) and expression of the potent eosinophilopoietic cytokine, interleukin-5 (IL-5). Therapy of SM and FIP1L1-PDGFRA-positive disease and the prognostic relevance of increased peripheral blood and tissue mast cells in hematolymphoid malignancies will also be addressed.

Wu Y, Chen C, Sun X, et al.
Cyclin-dependent kinase 7/9 inhibitor SNS-032 abrogates FIP1-like-1 platelet-derived growth factor receptor α and bcr-abl oncogene addiction in malignant hematologic cells.
Clin Cancer Res. 2012; 18(7):1966-78 [PubMed] Related Publications
PURPOSE: The "gate-keeper" mutations T674I platelet-derived growth factor receptor α (PDGFRα) in hypereosinophilic syndrome (HES) and T315I Bcr-Abl in chronic myeloid leukemia (CML) are resistant to imatinib and the second-generation small-molecule tyrosine kinase inhibitors (TKI). However, to combat acquired resistance to imatinib, an alternative approach is to decrease the expression of the addicted gene to efficiently kill resistant malignant hematologic cells. The purpose of this study was to evaluate the strategy of shutting down the transcription and expression of FIP1-like-1 (FIP1L1)-PDGFRα and Bcr-Abl with SNS-032, an inhibitor of cyclin-dependent kinase 7 (CDK7) and CDK9 in phase I clinical trials.
EXPERIMENTAL DESIGN: The effects of SNS-032 on PDGFRα and Bcr-Abl signaling pathways, apoptosis, and cell cycling were analyzed in TKI-resistant cells of HES and CML. The in vivo antitumor activity of SNS-032 was assessed with xenografted BaF3-T674I FIP1L1-PDGFRα and KBM5-T315I Bcr-Abl cells in nude mouse models.
RESULTS: SNS-032 inhibited the phosphorylation on Ser5 and Ser2 of RNA polymerase II. SNS-032 decreased both the mRNA and protein levels of FIP1L1-PDGFRα and Bcr-Abl and inhibited the proliferation of malignant cells expressing FIP1L1-PDGFRα or Bcr-Abl. It also decreased the phosphorylation of downstream molecules. It induced apoptosis by triggering both the mitochondrial pathway and the death receptor pathway.
CONCLUSIONS: This CDK7/9 inhibitor potently inhibits FIP1L1-PDGFRα-positive HES cells and Bcr-Abl-positive CML cells regardless of their sensitivity to imatinib. SNS-032 may have potential in treating hematologic malignancy by abrogating oncogene addiction.

Montano-Almendras CP, Essaghir A, Schoemans H, et al.
ETV6-PDGFRB and FIP1L1-PDGFRA stimulate human hematopoietic progenitor cell proliferation and differentiation into eosinophils: the role of nuclear factor-κB.
Haematologica. 2012; 97(7):1064-72 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: ETV6-PDGFRB (also called TEL-PDGFRB) and FIP1L1-PDGFRA are receptor-tyrosine kinase fusion genes that cause chronic myeloid malignancies associated with hypereosinophilia. The aim of this work was to gain insight into the mechanisms whereby fusion genes affect human hematopoietic cells and in particular the eosinophil lineage.
DESIGN AND METHODS: We introduced ETV6-PDGFRB and FIP1L1-PDGFRA into human CD34(+) hematopoietic progenitor and stem cells isolated from umbilical cord blood.
RESULTS: Cells transduced with these oncogenes formed hematopoietic colonies even in the absence of cytokines. Both oncogenes also stimulated the proliferation of cells in liquid culture and their differentiation into eosinophils. This model thus recapitulated key features of the myeloid neoplasms induced by ETV6-PDGFRB and FIP1L1-PDGFRA. We next showed that both fusion genes activated the transcription factors STAT1, STAT3, STAT5 and nuclear factor-κB. Phosphatidylinositol-3 kinase inhibition blocked nuclear factor-κB activation in transduced progenitor cells and patients' cells. Nuclear factor-κB was also activated in the human FIP1L1-PDGFRA-positive leukemia cell line EOL1, the proliferation of which was blocked by bortezomib and the IκB kinase inhibitor BMS-345541. A mutant IκB that prevents nuclear translocation of nuclear factor-κB inhibited cell growth and the expression of eosinophil markers, such as the interleukin-5 receptor and eosinophil peroxidase, in progenitors transduced with ETV6-PDGFRB. In addition, several potential regulators of this process, including HES6, MYC and FOXO3 were identified using expression microarrays.
CONCLUSIONS: We show that human CD34(+) cells expressing PDGFR fusion oncogenes proliferate autonomously and differentiate towards the eosinophil lineage in a process that requires nuclear factor-κB. These results suggest new treatment possibilities for imatinib-resistant myeloid neoplasms associated with PDGFR mutations.

Further References

Cools J, DeAngelo DJ, Gotlib J, et al.
A tyrosine kinase created by fusion of the PDGFRA and FIP1L1 genes as a therapeutic target of imatinib in idiopathic hypereosinophilic syndrome.
N Engl J Med. 2003; 348(13):1201-14 [PubMed] Related Publications
BACKGROUND: Idiopathic hypereosinophilic syndrome involves a prolonged state of eosinophilia associated with organ dysfunction. It is of unknown cause. Recent reports of responses to imatinib in patients with the syndrome suggested that an activated kinase such as ABL, platelet-derived growth factor receptor (PDGFR), or KIT, all of which are inhibited by imatinib, might be the cause.
METHODS: We treated 11 patients with the hypereosinophilic syndrome with imatinib and identified the molecular basis for the response.
RESULTS: Nine of the 11 patients treated with imatinib had responses lasting more than three months in which the eosinophil count returned to normal. One such patient had a complex chromosomal abnormality, leading to the identification of a fusion of the Fip1-like 1 (FIP1L1) gene to the PDGFRalpha (PDGFRA) gene generated by an interstitial deletion on chromosome 4q12. FIP1L1-PDGFRalpha is a constitutively activated tyrosine kinase that transforms hematopoietic cells and is inhibited by imatinib (50 percent inhibitory concentration, 3.2 nM). The FIP1L1-PDGFRA fusion gene was subsequently detected in 9 of 16 patients with the syndrome and in 5 of the 9 patients with responses to imatinib that lasted more than three months. Relapse in one patient correlated with the appearance of a T674I mutation in PDGFRA that confers resistance to imatinib.
CONCLUSIONS: The hypereosinophilic syndrome may result from a novel fusion tyrosine kinase - FIP1L1-PDGFRalpha - that is a consequence of an interstitial chromosomal deletion. The acquisition of a T674I resistance mutation at the time of relapse demonstrates that FIP1L1-PDGFRalpha is the target of imatinib. Our data indicate that the deletion of genetic material may result in gain-of-function fusion proteins.

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