Somatic mutations in the calreticulin gene (<i>CALR</i>) are detected in approximately 70% of patients with essential thrombocythemia (ET) and primary or secondary myelofibrosis (MF), lacking the <i>JAK2</i> and <i>MPL</i> mutations.
Compared with PV and ET, the JAK2V617F and CALR mutated allele burden was significantly higher in PPV-MF and/or PET-MF, indicating a role for accumulation of mutated alleles in the process of transformation to MF.