ERBB2 and breast cancer: Breast cancer remains the second leading cause of death for women in the United States.1 The 20–30% incidence of overexpression of the epidermal growth factor receptor family tyrosine kinase ERBB2 (HER2, Neu) in breast cancer2, 3 has made it a prominent therapeutic target.4 ERBB2 signaling depends on its heterodimerization with another ERBB family member, often ERBB3 or ERBB1 (epidermal growth factor receptor), which leads to activation of the phosphoinositide 3-kinase-AKT pathway.