Bone marrow findings in blast phase of polycythemia vera.

Approximately 10% of patients with polycythemia vera (PV) transform to acute leukemia (blast phase) at 10 years after initial diagnosis of PV. The bone marrow pathologic, cytogenetic, and molecular features of blast phase have not been well characterized. In this study, we reviewed 422 PV patients over a period of 11 years and identified 58 patients who developed acute myeloid leukemia (blast phase) during the course of disease. We found that blast phase of PV was characterized by overt myelodysplasia (n = 51, 88%); moderate to severe myelofibrosis (33 of 45, 73%); an abnormal karyotype (n = 51, 88%) that was often complex karyotype (n = 42, 72%); and gene mutations involving TP53 (55%), TET2 (27%), and DNMT3A (25%). Patients with blast phase of PV had an aggressive clinical course, with a median overall survival of 4 months after onset of blast phase. Eleven patients had close follow-up from polycythemic phase to blast phase: Four patients showed dysplastic changes in the polycythemic phase, and three of them transformed to blast phase without a "middle phase" of post-PV myelofibrosis.We conclude that blast phase of PV is characterized by myelodysplasia, moderate to severe fibrosis, a high frequency of an abnormal and often complex karyotype, and frequentTP53mutation.