InCALR-mutated PMF persons, thrombocytosis is the dominant phenotype reflecting myeloproliferation; in PMF, reduced CXCR4 expression on CD34-positive cells is associated with disease activity and poor prognosis.19This implies that theVEGFArs3025020T-allele acts directly, or through tight linkage to another gene(s), to regulate myeloproliferation/disease activity in this setting. This evidence concerns the gene CXCR4 and Thrombocytosis.