The PCM1-JAK2 fusion (PCM1 exon 25-JAK2 exon 9) (Figure 4a) [57] may be expressed in MPN, MDS B-ALL, or AML, and has been associated with different levels of eosinophilia in both blood and BM [57,58,81]. This evidence concerns the gene JAK2 and myelodysplastic syndrome.