Prospective observational study to assess the prognosis of patients with myeloproliferative neoplasms in Japan (MPN-15): results of baseline analysis

Myeloproliferative neoplasms (MPNs) are clonal hematologic disorders characterized by proliferation of one or more myeloid lineages. Data from large-scale prospective studies in Japan remain limited. We conducted a multicenter, prospective observational study (MPN-15) for the Japanese Society of Hematology to assess clinical characteristics, mutation profiles, risk stratification, and treatment patterns of patients diagnosed with polycythemia vera (PV), essential thrombocythemia (ET), prefibrotic primary myelofibrosis (pre-PMF), and fibrotic PMF after 2016. A total of 1252 patients were enrolled (PV: 323; ET: 726; MF: 203). JAK2V617F mutations were detected in 96.8% of PV patients and approximately 60% of patients with other subtypes; CALR and MPL mutations were more common in ET, pre-PMF, and fibrotic PMF. Chromosomal abnormalities and symptom burden were highest in fibrotic PMF. Thrombotic and survival risk stratification revealed that most patients with PV and ET were high risk. Use of ruxolitinib was reported in 14% of PV and 34% of fibrotic PMF patients, with no serious adverse events. This study represents the first large-scale prospective MPN registry in Japan. Ongoing follow-up will provide critical insights into long-term outcomes and therapeutic optimization in the Japanese population.