Patients with myeloproliferative neoplasm (MPN) could have laboratory aspirin resistance and then increasing dose of aspirin from once daily to twice daily regimen is suggested. However, it is not routinely recommended to perform platelet function testing to determine aspirin resistance in MPN patients. Moreover, it is not known whether increasing dose of aspirin would always correct aspirin resistance and significantly prevent the thrombotic events in MPN patients. Therefore, this study aims to compare the efficacy of once daily versus twice daily aspirin in high-risk MPN patients with aspirin resistance. MPN patients with laboratory aspirin resistance will be included in this prospective randomized study and platelet function testing will be repeated at one and six months later. Clinical thrombosis and side effect from aspirin will be recorded for at least 2 years after intervention.

Inclusion criteria included adult (>=18 years) Philadelphia-negative MPN patients taking aspirin (81 mg/day). Exclusion criteria included concomitant active cancer, thrombocytopenia (platelet less than 50,000/uL), taking anticoagulant, platelet function test (LTA method) showing no aspirin resistance, active gastric disease, active bleeding. Termination criteria included not taking aspirin regularly, serious side effect from aspirin. Block of four randomization is used. LTA testing is repeated at month 1 and 6 in both arms. PFA200 method is also done at initial enrollment for comparison with LTA method. Follow-up outcome data of clinical thrombosis, bleeding complication and adverse events related with aspirin are collected. Comparative analysis of outcome data is performed between two arms.

Inclusion Criteria:

• Philadelphia negative Myeloproliferative neoplasms aged at least 18 years old

Exclusion Criteria:

• Concomitant other active malignancy or cured less than 6 months
• Platelet count less than 50,000/microL
• Receiving anticoagulant
• Active peptic ulcer
• Active bleeding or Planning to undergo procedure/operation with bleeding risk
• No laboratory aspirin resistance with LTA method

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1 Jan 2027 (start date) to 31 March 2027 (end date)

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