PV and its sister diseases constitute stem cell-derived clonal myeloproliferation that is characterized by three mutually-exclusive “driver” mutations: JAK2, CALR, and MPL, with respective distribution frequency of ~99, 0, and 0% for PV, 55, 22, and 3% for ET and 65, 20 and 7% for PMF2. Here, CALR is linked to acquired polycythemia vera.