CALR and myeloproliferative neoplasm: Myeloproliferative neoplasms (MPN) are a group of clonal malignant bone marrow (BM) diseases, originating from a hematopoietic stem cell (HSC) which acquired a MPN phenotypic driver mutation (i.e., in JAK2, CALR, or MPL), leading to constitutively active JAK-STAT signaling (1, 2).