CALR and myeloproliferative disorder: Essential thrombocythaemia (ET) is one of four chronic myeloproliferative neoplasms (MPN), characterised by clonal thrombocytosis [1]; approximately 85% of patients will have a pathognomonic driver mutation at presentation—JAK-2 (about 50%), CALR (about 30%) or MPL (about 5%) [2].