Myeloproliferative neoplasms (MPNs) operationally include essential thrombocythemia, polycythemia vera, primary myelofibrosis (PMF), and prefibrotic PMF. All 4 MPN variants might progress into blast-phase disease (MPN-BP). For essential thrombocythemia, reported risk factors for leukemic transformation include advanced age, extreme thrombocytosis, anemia, leukocytosis, and sequence variants/mutations involving TP53 and EZH2 (for expansion of gene symbols, see www.genenames.org); for polycythemia vera, advanced age, leukocytosis, abnormal karyotype, mutations involving SRSF2 and IDH2, and treatment with pipobroman, chlorambucil, or P32; and for PMF, increased blast percentage, thrombocytopenia, abnormal karyotype, triple-negative driver mutational status, and sequence variants/mutations involving SRSF2, RUNX1, CEBPA, and SH2B3. The reported median survival figures for MPN-BP range from 1.5 to 2.5 months in patients treated with supportive care only, from 2.5 to 10 months in those receiving hypomethylating agents or low-dose chemotherapy, and from 3.9 to 9.4 months in those receiving induction chemotherapy. Three-year survival after allogeneic stem cell transplant was reported in 16% to 33% of patients. These observations validate the extremely poor prognosis associated with MPN-BP and the lack of effective drug therapy and highlight the need for urgent assessment of therapeutic values of investigational agents. In the meantime, affected patients might be best served with aggressive chemotherapy followed by allogeneic stem cell transplant after adequate blast clearance.