The ErbB (Erythroblastic Leukemia Viral Oncogene Homolog) or EGF (Epidermal Growth Factor) family of transmembrane RTKs (Receptor Tyrosine Kinases) plays an important role during the growth and development of a number of organs including the heart, the mammary gland, and the central nervous system. In addition, ErbB overexpression is associated with tumorigenesis of the breast, ovaries, brain, and prostate gland. The ErbB family includes four members, EGFR (EGF Receptor)/ErbB1/Her1 (Heregulin-1), ErbB2/Her2 (Heregulin-2), ErbB3/Her3 (Heregulin-3), and ErbB4/Her4 (Heregulin-4) (Ref.1). Two of the family members, ErbB1 and ErbB2, are involved in the development of many types of human cancer. All ErbBs have in common an extracellular ligand-binding domain, a single membrane-spanning region, and a cytoplasmic protein tyrosine kinase domain (Ref.2). Although these [...]