JAK2 and primary myelofibrosis: Mutations in the CALR gene have been identified in myeloproliferative neoplasms (MPNs), namely Type I (del52bp) and Type II (Ins5bp) mutations, the most common ones among essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients in a mutual exclusive pattern with the JAK2 V617F mutation (4, 5).