Abstract
The definition of a tumor marker is broad, which covers a wide spectrum of biomacromolecules synthesized in excess concentration by a wide variety of neoplastic cells. Tumor markers can be normal endogenous products that are produced at a greater rate in cancer cells or the products of newly switched on genes that remained inactive in the normal cells. These markers consist of any products of either tumor itself or the host in reaction to tumor's presence that distinguishes malignant tissues from benign and is measurable in body fluids or tissues. They increase with progressive or recurrent disease, decrease with response to treatment, and normalize with remission. Clinical applications include screening in asymptomatic individuals, confirming a suspected diagnosis, assisting in tumor classification and staging, prognosis, monitoring treatment response, surveillance for residual disease, and early detection of recurrent disease.