Targeted Therapies in HER2-Positive Breast Cancer - a Systematic Review

About 20% of all breast cancer patients have a human epidermal growth factor receptor 2 (HER2)-positive breast tumor. This entity underwent an impressive change in prognosis, with notable improvement of progression- free survival and overall survival. Due to more aggressive tumors and no specific therapy, HER2 overexpression was historically seen as a negative prognostic marker, with worse prognosis and increased risk of recurrent disease. Trastuzumab, the first anti-HER2 antibody, revolutionized the systemic therapy options in HER2-positive breast cancer and initiated several targeted therapies and more personalized treatment strategies. Over the years, multiple HER2-targeting drugs stepped into clinical practice, for the curative as well as the metastatic situation. This review summarizes the targeted treatment options in HER2-positive breast cancer and their current impact in the clinical routine. Results of the most outstanding trials in HER2-targeted therapies and important ongoing trials are subsequently described for an up-to-date overview.