Breast cancer starts when cells in the breast begin to grow out of control. These cells usually form a tumor that can often be seen in an x-ray or felt as a lump. The tumor is malignant if the cells invade the surrounding tissues or metastasize to distant organs of the body. In the last ten years, various new drugs have been introduced in the international markets to treat breast cancer. These drugs are administered either orally or via an injection. In this review, an insight is provided into the different signal transduction pathways that are being targeted for the purpose of adjuvant breast cancer treatment by the use of hormone-blocking agents, chemotherapy and monoclonal antibodies.