In a study of 132 patients (including 98 ET patients), we have documented varying degrees of platelet hyperactivity in 115 patients (87 ET patients) and a thrombosis-free survival rate of 1–23 years (median 8 years) whilst on the individualised anti-platelet therapy [15]; no significant differences were noted in terms of aspirin dose requirements (ranging from 100 mg twice or thrice weekly to 400 mg daily) between JAK-2, CALR- or MPL-positive patients and among the four IPSET-thrombosis [18,19] sub-groups. Here, CALR is linked to deep vein thrombosis.