The most evident demonstration for a pathological role of CALR in cancer etiology is provided by the observation that mutations in exon 9 of CALR are found in the Philadelphia-negative myeloproliferative neoplasms essential thrombocythemia and primary myelofibrosis lacking JAK2V617F mutations (Klampfl et al., 2013; Nangalia et al., 2013; Nunes et al., 2015). Here, CALR is linked to primary myelofibrosis.