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Polycythemia vera (PV) is a Philadelphia chromosome-negative chronic myeloproliferative neoplasm that is associated with a Janus kinase 2 (JAK2) mutation in most cases. The most recent update to the World Health Organization diagnostic criteria for PV was published in 2016. These were the modifications with the greatest effect: (1) lowering the hemoglobin threshold, allowing a diagnosis of PV at 16.5 g/dL in males and at 16.0 g/dL in females and (2) introducing a hematocrit cutoff (49% in males and 48% in females). Patients with PV who are older than 60 years or have had a previous thrombotic event are considered at high risk for thrombosis. Leukocytosis and a high allele burden are additional risk factors for thrombosis and myelofibrosis, respectively. After disease has progressed to post-polycythemia vera myelofibrosis (PPV-MF), survival must be assessed according to the recently developed Myelofibrosis Secondary to PV and ET-Prognostic Model (MYSEC-PM). This model is based on age at diagnosis, a hemoglobin level below 11 g/dL, a platelet count lower than 150 × 109/L, a percentage of circulating blasts of 3% or higher, a CALR-unmutated genotype, and the presence of constitutional symptoms. Therapy is based on phlebotomy to maintain the hematocrit below 45% and (if not contraindicated) aspirin. When a cytoreductive drug is necessary, hydroxyurea or interferon can be used as first-line therapy, although the demonstration of an advantage of interferon over hydroxyurea is still pending. In patients whose disease fails to respond to hydroxyurea, ruxolitinib is a safe and effective choice.

Transformation to secondary myelofibrosis (MF) occurs as part of the natural history of polycythemia vera (PPV-MF) and essential thrombocythemia (PET-MF). Although primary (PMF) and secondary MF are considered similar diseases and managed similarly, there are few studies specifically focused on the latter. The aim of this study was to characterize the mutation landscape, and describe the main clinical correlates and prognostic implications of mutations, in a series of 359 patients with PPV-MF and PET-MF. Compared with PV and ET, the JAK2V617F and CALR mutated allele burden was significantly higher in PPV-MF and/or PET-MF, indicating a role for accumulation of mutated alleles in the process of transformation to MF. However, neither the allele burden nor the type of driver mutation influenced overall survival (OS), while absence of any driver mutation (triple negativity) was associated with significant reduction of OS in PET-MF, similar to PMF. Of the five interrogated subclonal mutations (ASXL1, EZH2, SRSF2, IDH1, and IDH2), that comprise a prognostically detrimental high molecular risk (HMR) category in PMF, only SRSF2 mutations were associated with reduced survival in PET-MF, and no additional mutation profile with prognostic relevance was highlighted. Overall, these data indicate that the molecular landscape of secondary forms of MF is different from PMF, suggesting that unknown mutational events might contribute to the progression from chronic phase disease to myelofibrosis. These findings also support more extended genotyping approaches aimed at identifying novel molecular abnormalities with prognostic relevance for patients with PPV-MF and PET-MF. Am. J. Hematol. 91:681-686, 2016. © 2016 Wiley Periodicals, Inc.