Therefore, it is important to understand that it is the quantity and not just the presence of these compounds that must be considered in assessing the clinical use of tumour markers.
Tumour markers are usually proteins (structural proteins and enzymes), cell-surface carbohydrate antigens, cellular receptors, and genes, which are detected in tissue, urine, and blood samples. Markers can be specific for a certain type of cancer, while there are markers that are common for different cancer types. Some markers also show increased concentration in the tissues and body fluids even in the absence of cancers. Due to this, tumour markers by alone should not be used in to diagnose cancer.
In an ideal situation, screening and early diagnosis of cancer are the major goals for using tumour markers. To be able to do this, a marker must be highly specific for a certain cancer. It must not come up with too many false positive results that could lead to unnecessary and expensive follow-up tests, not to mention the psychological effects that come with the possibility of having cancer. Markers levels should be elevated enough, and ideally can be used to screen asymptomatic individuals, meaning that they can be used to detect cancer early. However, because markers are present in low concentrations in the body, screening for asymptomatic individuals is only recommended for those who have a genetic predisposition towards getting cancer. Currently, only the Prostate Specific Antigen (PSA) has been recommended and approved for general screening of prostate cancer in men over 50. A positive screening result for PSA is still not an indication of cancer, and PSA screening should be done in conjunction with a digital rectal examination of the prostate gland for diagnostic purposes.
Markers are used to identify the local source of metastasized cancers, and could therefore aid in making a correct diagnosis. The recurrence of cancer can be checked by testing the levels of a