CALR and acquired polycythemia vera: Polycythemia vera (PV) and essential thrombocythemia (ET) are BCR::ABL1 negative myeloproliferative neoplasms (MPNs) characterized by overproduction of one or more mature myeloid cell lineages, presence of Janus Kinase 2 (JAK2), calreticulin (CALR) or myeloproliferative leukemia virus (MPL) gene mutations, chronic inflammatory state, debilitating constitutional symptoms, and high thrombotic risk [1].