BCR and primary myelofibrosis: MPNs are characterized by differential myeloid cell proliferation that manifest as eight different forms, with Philadelphia chromosome (encoding the BCR-ABL fusion protein) positive chronic myeloid leukemia (CML) and the BCR-ABL negative diseases polycythemia vera (PV), essential thrombocytopenia (ET), and primary myelofibrosis (PMF) being the most common [1].