Trastuzumab emtansine in the treatment of HER-2-positive metastatic breast cancer patients.

The introduction of trastuzumab in the treatment of HER-2-positive metastatic breast cancer patients favorably changed the natural history of this disease. First-line treatment with trastuzumab and taxanes demonstrated a significant improvement in overall survival and progression-free survival compared with taxane alone. Despite such a major advance, HER-2-positive metastatic breast cancer will eventually progress in most patients. Moreover chemotherapy-associated toxicities, such as myelosuppression (docetaxel) and neurotoxicity (paclitaxel), may hamper the possibility to adequately treat metastatic breast cancer and may have a negative effect on patients' quality of life. The need for more effective and better-tolerated therapy for HER-2-positive metastatic breast cancer led to the development of new anti-HER-2 agents. Pertuzumab and trastuzumab emtansine are two of the new agents that will change the approach to the treatment of HER-2-positive metastatic breast cancer. Pertuzumab is a humanized monoclonal antibody that binds HER-2 at a different epitope of the HER-2 extracellular domain (subdomain II) than that at which trastuzumab binds. Trastuzumab emtansine is a HER-2-targeted antibody-drug conjugate, composed of the cytotoxic microtubule polymerization inhibitor DM1 that is conjugated to the monoclonal antibody trastuzumab, able to selectively deliver a cytotoxic agent to HER-2-positive tumor cells. TDM-1 is superior and less toxic than lapatinib plus capecitabine in metastatic breast cancer patients previously treated with trastuzumab and taxanes, and its role as a first-line therapy is currently under investigation.