EPO and acquired polycythemia vera: JAK2V617F-mediated cellular transformation seems to involve activation of JAK2-STAT3, JAK2-STAT5, ERK1/2 MAPK, and PI3K/AKT downstream signal transduction pathways, as: (i) STAT3 and BCLX overexpression are characteristic findings in human PV, (ii) human hematopoietic progenitors expressing constitutively active STAT5 and its target BCLX undergo EPO-independent colony formation, and (iii) hematopoietic transformation in murine bone marrow by TEL-JAK2 requires STAT5 [52].