MPL and essential thrombocythemia: Somatic mutation of JAK2, CALR, or MPL is found in 90% of the patients with ET.[1] The World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia uses the following criteria to diagnose ET: platelet count ≥ 450 × 109/L, increase in bone marrow megakaryocyte counts but not in the counts of other lineages, presence of clonal markers, and not meeting the WHO criteria for other hematologic diseases, with a more detailed description.[2]