Myeloid Neoplasma with Eosinophilia (MLN-Eo) with Rearrangement of JAK2 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 to a myeloid or lymphoid blast phase (with a corresponding unfavorable prognosis).

Note: In myeloid neoplasia with eosinophilia (MLN-Eo) with rearrangement of JAK2, the reciprocal translocation t(8;9)(p22;p24) is usually associated with a PCM1-JAK2 fusion gene (Reiter A et al. (2005). Much rarer are the ETV6-JAK2 and BCR-JAK2 fusion genes.

The clinical course is aggressive with primary blast phase or rapid progression to secondary blast phase.

The bone marrow morphology shows pathognomonic large paratrabecularly located clusters of predominantly immature proerythroblasts.

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