Emerging Therapeutic Options for HER2-Positive Breast Cancer

The natural history of HER2-positive breast cancer has progressively improved since the introduction of the first anti-HER2 directed therapy (trastuzumab). Trastuzumab has significantly increased survival of patients with HER2-positive metastatic breast cancer and, after the standardization of the use of this drug in the adjuvant setting in 2005, has also avoided many disease recurrences and, consequently, saved many lives. Later on, the introduction of lapatinib offered new choices for patients with advanced HER2-positive breast cancer, although the drug has failed to show a clear efficacy in the adjuvant setting. New promising drugs have been approved to broaden the horizon of HER2-positive breast cancer such as pertuzumab or T-DM1, but we need new options to further improve the management of these diseases. In this review, we cover new strategies that are currently under evaluation for the treatment of patients with HER2-positive breast cancer, including new tyrosine kinase inhibitors (neratinib, ONT-380), new antibody-drug conjugates targeting HER2 (MM-302), and new indications of already approved drugs (T-DM1), as well as the potential dual combinations of anti-HER2 therapy with phosphoinositide 3-kinase/mTOR or cell cycle inhibitors (palbociclib, abemaciclib). Last but not least, we briefly review a new paradigm of emerging approaches that involve the host immune response, HER2 breast cancer vaccines, and other immune strategies, including immune checkpoint inhibition.