JAK2 and sarcoma: Earlier studies revealed that EPO expression was induced by hypoxia-inducible factor (HIF), and in erythroid progenitor cells, such as BFU-E and CFU-E cells, EPO and its receptor (EPOR) trigger canonical Janus kinase 2/signal transducer and activator of transcription 5 (JAK2/STAT5), rat sarcoma/mitogen-activated protein kinase/extracellular signal-regulated kinase (RAS/MEK/ERK), and phosphatidylinositol 3-kinase (PI3K) pathways [27].