Platelets from healthy donors (HD) and Essential Thrombocythemia (ET) patients were isolated from peripheral blood. The HD were treated with low dose aspirin (100mg) once daily and blood samples were collected before and after treatment. ET patients from different mutational backgrounds (JAK2 V617F, MPL W515K/L, CALR Type 1 &2) were either untreated or treated with aspirin, HU, anagrelide or a combination of them at the time of blood donation. Platelets were pelleted after centrifugation (1100rpm, no brake at room temperature) and were snap frozen in liquid nitrogen before stored to -80C for mass spectrometry.