Figure 1: Overview intracellular signal transduction pathways involved in the proliferation and progression of breast cancer. Targeted therapy agents discussed in this review and their main inhibition targets are illustrated. EGF: Epidermal growth factor; EGFR: EGF receptor; HGF: hepatocyte growth factor; c-MET: mesenchymal– epithelial transition factor; PDGF: Platelet-derived growth factor; PDGFR: PDGF receptor; IGF-1: insulin-like growth factor-I; IGF-1R: IGF-1 receptor; PI3K: phosphatidylinositol 3-kinase; Ras: Rat sarcoma subfamily of GTPases; AKT: protein kinases B; PDK1: pyruvate dehydrogenase kinase isozyme 1; mTOR: mammalian target of rapamycin; MEK: mitogen-activated protein kinase kinase; VEGF: vascular endothelial growth factor; VEGFR: VEGF receptor; BRAF: B-type RAF kinase; src: v-Src (Rous sarcoma virus) tyrosine kinase; BCRABL: Philadelphia chromosome; JAK/STAT: Janus kinases/signal transducers and activators of transcription; PTEN: phosphatase and tensin homolog; HDAC: histone deacetylases.