Tumor markers are molecules produced in the body in response to cancer. Tumor markers are molecules produced by tumor cells or other cells of the body in response to cancer or certain benign conditions. Most tumor markers are secreted into blood and may be estimated in blood, but they may also be measured in urine, tissues etc. Tumor markers may be used for diagnosis, staging, and prognosis of cancer; they may also be used for monitoring treatment response as well as to check for cancer recurrence. There are a large number of tumor markers which are used for different types of cancers; many tumor markers may also be elevated in more than one type of cancer.