They include Cell surface antigens; Cytoplasmic proteins, Enzymes, Hormones and most of them are proteins. They can be products of cancer cells themselves or of the body in response to cancer or other conditions. A marker represents a qualitative or quantitative alteration or deviation from normal of a molecule, substance, or process that can be detected by some type of assay. An elevated level of a tumor marker can indicate cancer; however there can also be other causes of the elevation. Thus, Tumour markers cannot be construed as primary modalities for the diagnosis of cancer. These tumor markers help in screening, diagnosing the diseased condition, staging of the disease, guiding and monitoring the treatment, to determine the prognosis and to prevent recurrence.