JAK2 and cancer: Grb2 is downstream of various oncogenic tyrosine kinases and participates in several signaling pathways, such as mitogen-activated protein kinase, breakpoint cluster region protein-Abelson murine leukemia viral oncogene homolog (BCR-ABL), KIT, fms related tyrosine kinase 3 (FLT3), and Janus kinase 2 (JAK2) tyrosine kinases, and is frequently overactivated in cancers [13,14].