EPO and myeloproliferative disorder: MPNs are clonal disorders with progressive accumulation of JAK2V617F‐mutated cells, which is attributed to an increased fitness of the mutant haematopoietic progenitors,6 a growth advantage of these progenitors in the presence of low erythropoietin (EPO) levels and to a selective advantage of JAK2V617F‐HSPCs in the context of the MPN microenvironment.1