EPO and myeloproliferative disorder: In MPNs, TPO and EPO levels are low or undetectable, but MPN patients have high blood levels of numerous inflammatory cytokines; some of these cytokines activate JAK2/STAT5 (G-CSF, granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 6 (IL-6)) while others activate the JAK1/STAT1/STAT3 pathways, notably IL-6 and interferons (IFN) [11,12].