ABSTRACT
HER2-positive breast cancer is an aggressive subtype of breast cancer with five-year survival rates of 30% for the advanced stage. The development of anti-HER2 treatments has led to a paradigm shift in the management and clinical outcomes of advanced HER2-positive breast cancer patients. The standard first-line treatment consists of taxane-based chemotherapy plus dual anti-HER2 therapies with trastuzumab and pertuzumab. The antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1) has been a second-line therapeutic standard, but the second-line treatment approach is rapidly evolving. Given a substantial advantage of another ADC, Fam-trastuzumab deruxtecan (T-DXd), compared to T-DM1 in a recent randomized trial in the second-line setting, T-DXd is currently the preferred second-line option. Optimal third-line treatment strategies are still not established, and multiple approaches have been used including combinations based on capecitabine, trastuzumab, or both with oral anti-HER2 tyrosine kinase inhibitors. Tucatinib plus capecitabine and trastuzumab, lapatinib plus trastuzumab, neratinib or lapatinib plus capecitabine are some of the FDA approved combinations. Another newer agent approved for third- or later-line therapy in the metastatic setting is margetuximab, an Fc-engineered anti-HER2 monoclonal antibody, in combination with chemotherapy. Other novel agents currently under clinical trials are the drugs that indirectly target HER2, including immune cell cycle inhibitors, PI3K/mTOR inhibitors, and immunotherapy agents.