According to the American Cancer Society, tumor markers are substances that are found in the body when cancer is present. These substances are usually in the blood, although they can be in tissues and the tumor itself. There are many different tumor markers, but only some are used because most of these markers can be made by things other than cancer. Tumor markers are used alongside physical exam and other diagnostic tests in the diagnosis and management of cancers, and can be helpful in evaluating the cancer's response to treatment.
Prostate-Specific Antigen (PSA)
PSA is a tumor marker for prostate cancer, and is the only tumor marker that is used as a screening tool for a specific cancer. PSA is a protein made by the prostate gland, and levels of this protein are often elevated in prostate cancer, although other factors may also increase PSA levels, such as older age and inflammation of the prostate. A digital rectal exam is typically performed along with the PSA test when screening for prostate cancer, and this tumor marker is often used in the follow-up of men with prostate cancer to check for recurrence and response to treatment.
CA-125
CA-125 levels are typically used with women in treatment or post-treatment for ovarian cancer. Rising levels of this tumor marker can mean the cancer is returning or not responding to treatment. The CA-125 marker is not used as a screening test because early ovarian cancers would likely be missed, and other problems like uterine fibroids and endometriosis can cause high CA-125 levels.
Alpha Feto-Protein (AFP)
The AFP tumor marker is used when diagnosing liver cancer and its treatment, because most patients with liver cancer have elevated AFP levels. This protein can also be elevated with some kinds of testicular cancer and can be used in the follow-up of these cancers as well. During treatment, the AFP levels can be followed to see how the cancer is responding to treatment.
Carcinoembryonic Antigen (CEA)
CEA is a tumor marker that can help predict prognosis in patients with colorectal cancer, although it is not used in the diagnosis or screening of the disease. This marker is also used to gauge how the cancer is responding to treatment. CEA can also be elevated in other cancers, and can be used to follow treatment response if the CEA was high at the time of diagnosis.
