Breast cancer, as one of the most frequent tumor entities, is the object of intensive research activity. Clinical research over the last few years has resulted in an increasing differentiation in treatment strategies in the adjuvant setting as well as in metastatic breast cancer. Treatment decision is guided by different risk groups, and relevant changes in clinical practice have arisen in hormonal treatment as well as in chemotherapy. Furthermore, new agents have shown clinical activity, in particular trastuzumab has emerged as standard treatment in HER2 positive breast cancer. It was even licensed in 2006 for adjuvant treatment.