Endocrine therapy and chemotherapy (using either sequential single agents or combination regimens) remain the principal treatments for women with metastatic breast cancer. A wide variety of classes of chemotherapeutic agents have demonstrated anti-tumor activity as single agents or in combination regimens. Cytotoxic chemotherapeutic agents have been the mainstay of cancer therapies for many years and have improved survival in many disease settings. Median survivals remain approximately two years for women with metastatic breast cancer, and less than 3% of patients experience long-term survival after initiation of treatment. The development of new treatment strategies is therefore essential to improve outcome for patients with metastatic breast cancer.