Although the ErbB2 receptors lack a ligand binding site and the ErbB3 receptor has no tyrosine kinase activity, these receptors can initiate signal transduction by undergoing homo- or heterodimerization [10,11] and are particularly potent in activating PI3K/Akt and Ras/mitogen activated protein kinase (MAPK) mitogenic signaling pathways, and elevated PI3K/Akt and MAPK activity is associated with advanced tumor progression and poor prognosis in breast cancer patients [6,9,12,13]. The gene discussed is AKT1; the disease is breast cancer.