The translocation t(8;9)(p22;p24) results in the production of a chimeric PCM1-JAK2 fusion protein leading to the constitutive activation of the Janus Kinase 2 that renders this disease potentially sensitive to ruxolitinib. Here we report an interesting case of PCM1-JAK2 myeloproliferative neoplasm evolving in myeloid sarcoma and B precursor ALL.