Myeloid Neoplasma with Eosinophilia (MLN-Eo) with Rearrangement of PDGFRB D72.1, C47.5

Myeloid neoplasms with eosinophilia are a clinically, morphologically, genetically, and prognostically heterogeneous group of clonal diseases characterized as follows:

• Initially, a persistent proliferation of clonal eosinophilic granulocytes in the peripheral blood.
• a hypercellular bone marrow
• if necessary, splenomegaly (Valent Pet al. 2012).

In morphology, the assessment of qualitative and quantitative changes in the non-eosinophil series (megakaryocytes, monocytes, mast cells, blasts) and bone marrow fibrosis is significant. By means of molecular genetic investigations, cytogenetic aberrations (e.g. reciprocal translocation, deletion, inversion, trisomy, complex karyotype), rearrangements of genes (FISH analysis), fusion genes (FISH analysis, RT-PCR) or mutations (allele-specific PCR, NGS) are included in the diagnosis. The causative genetic aberrations are characterized by a varying risk of progression into a myeloid or lymphoid blast phase (with a correspondingly unfavorable prognosis).

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Peripheral eosinophilia may be absent in up to 20% of patients. Since monocytosis >1000/µl is present in peripheral blood in about 30% of patients, CMML, atypical CML or JMML may be diagnosed. Splenomegaly is common, whereas other organs are affected less frequently than in FIP1L1-PDGFRA. Bone marrow findings are comparable to those in FIP1L1-PDGFRA fusion gene (hypercellular, proliferation of mast cells, concurrent diagnosis of MPN in bone marrow with lymphoma in lymph node biopsy).

Diagnosis is made by detection of rearrangement of PDGFRB by FISH analysis and (subsequent) detection of the fusion gene by RT-PCR/FISH analysis;

Note: Rearrangement of chromosome band 5q31-33 leads to fusion of PDGFRB tyrosine kinase with more than 30 different fusion partners. The most common fusion genes are ETV6-PDGFRB and CDCC88C-PDGFRB (Reiter A et al. 2017).

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