HER2-directed therapy for metastatic breast cancer.

Human epidermal growth factor receptor 2 (HER2) overexpression drives the biology of 20% of breast cancers, and predicts a poor prognosis for patients. HER2-targeted therapies significantly improve outcomes for HER2-positive patients with both early and metastatic breast cancer. Currently three HER2-targeted agents, trastuzumab (Herceptin), lapatinib (Tykerb), and pertuzumab (Perjeta), are available for the treatment of HER2-positive metastatic breast cancer (MBC). Numerous studies have attempted to optimize their use by combining them with each other, or with endocrine and cytotoxic therapies. Most recently, the FDA approved the combination of trastuzumab, pertuzumab, and docetaxel as first-line treatment for MBC, and in late February 2013 approved a fourth HER2-targeted agent, trastuzumab emtansine (T-DM1, Kadcyla), for accelerated approval. These advances create a number of clinical dilemmas, including identification of the optimal sequence of HER2-targeted agents and the best drug combinations to use, as well as the recognition of primary and acquired drug resistance. In this article, we review clinical data informing the effective management of HER2-positive MBC.