Platelets from three healthy donors (HD) and eighteen Essential Thrombocythemia (ET) patients were isolated from peripheral blood. The three 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, and CALR Type I & II) were either untreated or treated with aspirin at the time of blood donation. Pellets were pelleted after centrifugation (1100rpm, no brake at room temperature) and were snap frozen in liquid nitrogen before stored to -80C for mass spectrometry.