Cancer is caused by genetic mutations---which can be inherited or acquired over time---that lead to cells growing abnormally quickly (causing tumors) and developing the ability to invade other tissues. Because tumor cells are different than normal cells, they can cause changes in the body that can be detected by some blood and urine tests.
Identification
Cancer markers (also known as tumor markers) are chemicals that can be produced either by tumor cells or by the human body in response to certain cancers. The National Cancer Institute notes that sometimes the levels of these chemicals are measured to screen for cancers. However, they are not a perfect test because cancer markers can be elevated by some noncancerous diseases.
Examples
MayoClinic.com notes that examples of cancer markers include prostate-specific antigen (PSA) and cancer antigen 125 (CA-125). These markers can be used to detect prostate cancer and ovarian cancers, respectively. Ovarian cancers can also increase the levels of a protein called human chorionic gonadotropin, which can also be measured as a cancer marker. Liver cancers, on the other hand, can cause increased levels of a protein called alpha-fetoprotein.
Testing
According to the American Cancer Society, cancer markers are usually measured from a sample of the patient's blood or urine. In these cases, the fluid sample is sent to a lab that measures the amount of the marker by exposing it to special proteins (called antibodies) that bind to the cancer marker. Sometimes samples of a tumor are also checked for cancer markers.
Uses
One way in which cancer markers can be used is to screen for cancers. This can be done if a patient is showing symptoms of a particular cancer or if the patient has a family history of these cancers. Some cancer markers can be used to predict how aggressively a cancer will grow; some rapidly dividing cancers have specific tumor markers. Cancer markers can also be used to monitor the effectiveness of a course of chemotherapy or radiation. If a form of cancer causes high levels of a tumor marker that is then reduced after chemotherapy, it generally indicates that the treatment is working.
Drawbacks
Cancer markers are a useful tool in the diagnosis and monitoring of some cancers, but there are shortcomings to this kind of analysis. Cancer markers are normally present (albeit in low levels) in healthy patients, which can make early detection of cancer difficult. Some patients with cancer never have high levels of any cancer marker. In addition, elevated levels of cancer markers can be due to noncancerous conditions.
