HER-3 functions as a co-receptor with other EGFR family members or other Tyrosine Kinase Receptors (RTK)s as such c-MET and IGFR, and activates downstream signaling pathways, mainly the PI3K-AKT and MAPK-ERK pathways, which are critical for cancer cell growth and survival [7, 8]. The gene discussed is ERBB3; the disease is cancer.