Following the 2001 WHO Classification, the molecular bases of myeloid tumors were deeply investigated with the discovery of JAK2 and MPL mutations in Philadelphia-negative CMPDs [18], KIT mutations in Mastocytosis [19], and PDGFRA, PDGFRB, and FGFR1 rearrangements in subsets of myeloid/lymphoid neoplasms with eosinophilia [20]. This evidence concerns the gene JAK2 and myeloid neoplasm.