Myelofibrotic and leukemic transformation in 2016 WHO-defined Philadelphia-negative myeloproliferative neoplasm

BACKGROUND: Information on myelofibrotic and leukemic transformations in Korean Philadelphia chromosome-negative myeloproliferative neoplasms (Ph(‒) MPNs) is limited. METHODS: This study retrospectively analyzed transformations in patients diagnosed with essential thrombocythemia (ET), polycythemia vera (PV) prefibrotic/early primary myelofibrosis (pre-PMF), or overt primary myelofibrosis (PMF) based on the 2016 World Health Organization criteria between January 1996 and December 2020 at Chungam National University Hospital, Daejeon, Korea. RESULTS: A total of 351 patients (144 with ET, 131 with PV, 45 with pre-PMF, and 31 with PMF; 204 men and 147 women) with a median age of 64 years (range, 15‒91 years) were followed for a median of 4.6 years (range, 0.2‒24.8 years). The 10-year incidence of overt myelofibrosis was higher in pre-PMF than in ET (31.3% and 13.7%, respectively; P=0.031) and PV (12.2%; P=0.003). The 10-year incidence of leukemic transformation was significantly higher in PMF than in ET (40.0% and 7.9%, respectively; P=0.046), pre-PMF (4.7%; P=0.048), and PV (3.2%; P=0.031). The 5-year incidence of leukemic transformation was higher in patients with secondary myelofibrosis (SMF) than in those with PMF (19.0% and 11.4%, respectively; P=0.040). The 5-year overall survival of patients with SMF was significantly worse than that of patients with pre-PMF (74% and 93%, respectively; P=0.027) but did not differ from that of patients with PMF (57%; P=0.744). CONCLUSION: The rates and clinical courses of myelofibrotic and leukemic transformations in Korean patients with Ph(‒) MPN did not differ from those in Western populations.