ERBB2 and cancer: The insulin-like growth factor 1 (IGF-I) receptor, insulin receptor, and HER2 act through the same downstream signaling pathway via phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR; the presence of interactions at multiple levels between PI3K/AKT/mTOR, estrogen, growth factor signaling, and the receptor tyrosine kinase cascade stimulates cancer cell proliferation and survival.