This study demonstrates the utility of screening for PDGFRA kinase domain overexpression in patients with IHES and has identified a third PDGFRA fusion partner in chronic myeloproliferative disorders.
This study also found losses at 11q13.3 in 26% of patients with MPN-Ph- and in 19p13.11 in two of the three patients with an MPN associated with a PDGFRA rearrangement.
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.
The revised 2008 WHO classification system featured the following changes: 1) the term "CMPD" was replaced by "myeloproliferative neoplasm (MPN)," 2) mast cell disease was formally included under the category of MPN, and 3) the subcategory of CEL/HES was reorganized into "CEL not otherwise specified (CEL-NOS)" and "myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, and FGFR1"; CEL-NOS remained a subcategory of "MPN," whereas the latter neoplasms were now assigned a new category of their own.
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.
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.
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.
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.
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.
However, although the incidence of MPD involving translocations of PDGFRB has been well established, to our knowledge there are only two previous reports describing a BCR-PDGFRA fusion gene, in 3 patients diagnosed with atypical CML.
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.