Tumor markers are substances produced by the tumors or by other cells of the body in response to cancer or certain benign conditions. Although most of these markers are made by the normal cells as well as by cancer cells, they are produced at much higher levels in cancerous conditions. These markers are used to evaluate the patient's response to treatment and to detect the presence of metastasis or recurrence. Breast cancer is one of the most common malignancies in females worldwide. The CA 27-29, CA 15-3, CA27.29, carcinoembryonic antigen, tissue polypeptide specific antigen, p53, cathepsin D, cyclin E, nestin and HER-2 are tumor markers that are often expressed in people with breast cancer. They play a crucial role in diagnosis, monitoring response to therapy, early detection of metastasis and determination of recurrence in patients with breast cancer.