<i>MPL</i> gene mutation is a possible risk factor for thrombosis in patients with essential thrombocythemia in Japan

Since <i>MPL</i> mutation is a rare driver gene mutation found in a small number of essential thrombocythemia (ET) patients, the clinical characteristics of patients with <i>MPL</i> mutations and their association with thrombotic events have not yet been elucidated in Japan. We enrolled 579 Japanese ET patients based on the diagnostic criteria of the WHO classification 2017 and compared clinical characteristics of <i>MPL</i>-mutated patients (<i>n</i> = 22; 3.8%) to <i>JAK2</i>V617F-mutated (<i>n</i> = 299; 51.6%), <i>CALR</i>-mutated (<i>n</i> = 144; 24.9%), and triple-negative (TN) (<i>n</i> = 114; 19.7%) patients. Thrombosis during follow up was observed in 4 out of 22 (18.2%) in the <i>MPL</i>-mutated group, which was the highest among all driver gene mutation groups (<i>JAK2</i>V617F-mutated, 8.7%; <i>CALR</i>-mutated, 3.5%; TN,1.8%). The <i>MPL-</i> and <i>JAK2</i>V617F-mutated groups had worse thrombosis-free survival (TFS) than the <i>CALR</i>-mutated (<i>p</i> = 0.043) and TN groups (<i>p</i> = 0.006). Univariable analysis revealed that a history of thrombosis was a possible risk factor for thrombosis among <i>MPL</i>-mutated patients (hazard ratio: 9.572, <i>p</i> = 0.032). <i>MPL</i>-mutated ET patients should require more intensive management to prevent recurrence of thrombosis.