JAK2 is an intra-cytoplasmic tyrosine kinase that belongs to the Janus kinase family. JAK kinases play a major role in the transmission of signals from cytokine and growth factor receptors into the nucleus. JAK kinases activate several intracellular signaling proteins, among which the STAT transcription factors are well defined. The JAK/STAT pathway mediates diverse cellular events that affect cell growth, differentiation and cell survival.