Breast cancer is the most common cancer worldwide among women and the second most common cancer.Approximately 15-23% of breast cancers over-express human epidermal growth factor receptor2 (HER2), a185-kDa transmembrane tyrosine kinase, which is mainly found at the cell surface of tumor cells. HER2-positivebreast cancer, featuring amplification of HER2/neu and negative expression of ER and PR, has the three followingcharacteristics: rapid tumor growth, lower survival rate, and better response to adjuvant therapies. Clinically,it is notable for its role in a pathogenesis that is associated with increased disease recurrence and acts as a worseprognosis. At the same time, it represents a good target for anti-cancer immunotherapy despite the prevalenceof drug resistance. New treatments are a major topic of research, and a brighter future can be expected. Thisreview discusses the role of HER2 in breast cancer, therapeutic modalities available and prognostic factors.