What is the definition or description of: tumor marker?

Released by cancer: A tumor marker is a substance found in the blood urine or body tissues that can be elevated in cancer among other tissue types. There are many different tumor markers, each indicative of a particular disease process, and they are used in oncology to help detect the presence of cancer. An elevated level of a tumor marker can indicate cancer; however, there can also be other causes of the elevation.

The best: Example may be alpha-fetoprotein in testis. If it is there at diagnosis, and disappears, it is a reliable indicator of the tumor, and the tumor return may be heralded in a rise in the marker. Many others, cea, ca 125, ca 19-9 arevnot as reliable.