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]. The gene discussed is JAK2; the disease is acute lymphoblastic leukemia.