Current and emerging targeted therapies for metastatic breast cancer.

The success of endocrine therapies for hormone receptor-positive breast cancer and trastuzumab and lapatinib for targeting human epidermal growth factor receptor 2 (HER2)-positive tumors has paved the way for the clinical development of several other metastatic breast cancer (MBC)-targeted therapies. Although the benefit of the anti-VEGF (vascular endothelial growth factor) monoclonal antibody bevacizumab in the MBC setting has become a topic of debate, clinical trial results are accumulating, and phase 3 evaluations are ongoing for newer HER2-targeted agents (pertuzumab and trastuzumab-maytansine immunoconjugate) and VEGF-targeted agents (aflibercept), as well as dual, epidermal growth factor receptor/HER2-targeted agents (afatinib [BIBW 2992] and neratinib), multitargeted tyrosine kinase inhibitors (sunitinib and pazopanib), and mammalian target of rapamycin (everolimus) and poly (ADP-ribose) polymerase 1 inhibitors (iniparib, olaparib). These agents as well as other novel classes of anticancer agents are being tested in clinical trials with the potential of addressing unmet therapeutic needs in the MBC patient population.