CALR and acquired polycythemia vera: The CALR mutations are present almost exclusively in JAK2-V617F negative patients with ET and PMF [2–6], although cases of refractory anaemia with ring sideroblasts associated with thrombocytosis (RARS-T) and PV [7, 8], in addition to rare cases of JAK2-V617F or BCRABL1 co-positivity have been reported [9, 10].