PMF results from clonal expansion of myeloid cells and is characterized by the variable presence of the driver mutations JAK2, CALR, or MPL, other mutations such as ASXL1, SRSF2, and U2AF1, morphologically characteristic megakaryocyte proliferation that might or might not be accompanied by reactive bone marrow fibrosis, peripheral blood leukoerythroblastosis, anemia, marked hepatosplenomegaly, and constitutional symptoms2–4. This evidence concerns the gene CALR and anemia (phenotype).