Breast cancer has the highest incidence among those occurring in Korean women. Adjuvant treatment of breast cancer aims to reduce micro-metastatic foci and to prevent relapse after surgery. Four cycles of AC showed equal survival benefits compared with 6 cycles of CMF, and it is not clear if the addition of taxane improves the survival. Adjuvant hormonal therapy shows reduction of relapse rate and mortality rate in both pre and post-menopausal women, if hormone receptors are expressed in the tumor. Metastatic breast cancer shows 3~25% long-term survival after response to chemotherapy or hormonal therapy, and thus in this situation, it is very hard to expect cure. And in advanced and metastatic breast cancer, chemotherapy is indicated in hormone-resistant breast cancer patients. However, in patients with a low probability of hormone sensitivity, in patients with very rapid progression, and in those with extensive metastases in lungs or liver, chemotherapy is the treatment of choice. The new class of chemotherapeutic agents such as tyrosine kinase inhibitors are being developed and are tried for the treatment of breast cancer with the hope of improving QOL and prolonging survival. Pre-operative chemotherapy improved not only the survival but also the local control rate. Multidisciplinary approach is strongly recommended to improve the efficacy of various therapy tools for breast cancer treatment in Korea, and the very rapid development of new treatment modalities together with the markers predicting response and prognosis is expected in the near future.