Ripretinib (DCC-2618) was designed to inhibit the full spectrum of mutant KIT and PDGFRA kinases found in cancers and myeloproliferative neoplasms, particularly in gastrointestinal stromal tumors (GISTs), in which the heterogeneity of drug-resistant KIT mutations is a major challenge.
That ponatinib briefly induced remission in our patient with acute myeloid leukemia arising from a myeloproliferative neoplasm with eosinophilia and FIP1L1-PDGFRα fusion may merit exploration of ponatinib as a potential second-line treatment option for this patient population.
The purpose of this review is to provide an overview of the differential diagnosis for eosinophilia, to recommend specific steps for the pathologist evaluating blood and bone marrow, and to emphasize 2 important causes of eosinophilia that require specific ancillary tests for diagnosis: myeloproliferative neoplasm with PDGFRA rearrangement and lymphocyte-variant hypereosinophilic syndrome.
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.
In BCR-ABL1-negative myeloproliferative neoplasms (MPNs) several different tyrosine kinase fusion events have been described, most commonly involving the genes encoding the platelet-derived growth factor receptor alpha (PDGFRA) or beta (PDGFRB).
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.
The introduction of JAK2 mutation testing has changed dramatically the diagnostic algorithms for myeloproliferative neoplasms (MPNs) but there is still a place for conventional cytogenetic analysis in the initial work-up of MPN cases, particularly as this group of myeloid disorders has been expanded to include chronic eosinophilic leukaemia and myeloid neoplasms with abnormalities of the PDGFRA, PDGFRB, and FGFR1 genes.
Important changes include (1) the change of nomenclature of myeloproliferative disorder to myeloproliferative neoplasm emphasizing the clonal nature of these disorders; (2) the classification of mast cell disease as an MPN; (3) the reorganization of the eosinophilic disorders into a molecularly defined category of PDGFRA, PDGFRB and FGFR1-associated myeloid and lymphoid neoplasms with eosinophilia and chronic eosinophilic leukemia, not otherwise specified; and (4) refinement of the diagnostic criteria for PV, ET and PMF incorporating recently described molecular markers, JAK2V617F, JAK2 exon 12 mutations and MPL mutations.
This review highlights the important diagnostic tools in classical and atypical myeloproliferative neoplasms mainly the JAK2V617F mutation, the Mpl receptor, Polycythemia rubra vera 1 (PRV1), platelet-derived growth-factor receptor alpha (PDGFRA), platelet-derived growth-factor receptor beta (PDGFRB), fibroblast growth-factor receptor 1 (FGFR1) and c-kit tyrosine kinase.
Rapid identification of diverse fusion genes with involvement of PDGFRA or PDGFRB in eosinophilia-associated myeloproliferative neoplasms is essential for adequate clinical management but is complicated by the multitude and heterogeneity of partner genes and breakpoints.
Imatinib is usually a highly effective treatment for myeloproliferative neoplasms (MPNs) associated with ABL, PDGFRA or PDGFRB gene fusions; however, occasional imatinib-responsive patients have been reported without abnormalities of these genes.
Therapeutically validated oncoproteins in myeloproliferative neoplasms (MPNs) include BCR-ABL in chronic myelogenous leukemia (CML) and a spectrum of PDGFRA/B mutant proteins that are products of intra- (eg, FIP1L1-PDGFRA) or interchromosomal (eg, ETV6-PDGFRB) gene fusions.
We investigated genetically affected leukemic cells in FIP1L1-PDGFRA+ chronic eosinophilic leukemia (CEL) and in BCR-ABL1+ chronic myeloid leukemia (CML), two myeloproliferative disorders responsive to imatinib.
The FIP1L1-PDGFRA fusion gene is a recurrent molecular lesion in eosinophilia-associated myeloproliferative disorders, predicting a favorable response to imatinib mesylate.