Essential thrombocythemia (ET) is a myeloproliferative neoplasm (MPN) with approximately 40 to 60% of patients carrying the somatic V617F mutation in the Janus kinase 2 gene (JAK2) and 5% harbouring a substitution mutation in exon 10 of the thrombopoietin receptor gene (MPL). Recently, frameshift mutations located in exon 9 of the calreticulin (CALR) gene have been described in 70 – 85% of MPN patients without JAK2 or MPL mutations. Patients with ET harbouring a CALR mutation have a more indolent clinical course when compared to patients with the JAK2 V617F mutation. Approximately 10% of suspected ET cases may be JAK2, MPL or CALR negative and may have a mutation involving a yet to be discovered gene or one of the following genes: LNK, SOCS1, SOCS3, TET2, ASXL1.
This presentation will focus on the laboratory detection of JAK2 V617F, MPL W515 and CALR exon 9 mutations. Detection of these mutations in the peripheral blood of patients with suspected ET allows for the positive identification of this disorder in approximately 90% of patients; these mutations are not found in cases of reactive thrombocytosis.