ACS :: Tumor Markers

ACS :: Tumor Markers


Tumor Markers
What are tumor markers?
Tumor markers are substances that can be found in the body when cancer is present. They are most often found in the blood or urine, but they can also be found in tumors and other tissue. They can be products of the cancer cells themselves, or made by the body in response to cancer or other conditions. Most tumor markers are proteins.
There are many different tumor markers. Some are seen only in a single type of cancer, while others can be found in many types of cancer.
To test for a tumor marker, the doctor most often sends a sample of the patient's blood or urine to a lab. The marker is usually found by combining the blood or urine with man-made antibodies that react with the tumor marker protein. Sometimes a piece of the tumor itself is tested for tumor markers.
For many reasons, tumor markers alone cannot show if cancer is present. Most tumor markers can be made by normal cells as well as by cancer cells. Sometimes, non-cancerous diseases can also cause levels of certain tumor markers to be higher than normal. And not every person with cancer may have higher levels of a tumor marker.
For these reasons, only a few tumor markers are commonly used by most doctors. When a doctor looks at the level of a certain tumor marker, he or she will consider it along with the patient's history and physical exam and other lab tests or imaging tests.
In recent years, doctors have begun to develop newer types of tumor markers. With advances in technology, levels of certain genetic materials (DNA or RNA) can now be measured. It's been hard to identify single substances that provide useful information, but doctors are now beginning to look at patterns of genes or proteins in the blood. These new fields of genomics and proteomics are discussed in the section, "What's new in tumor marker research?"
How are tumor markers used?
Screening and early detection of cancer
Screening refers to looking for cancer in people who have no symptoms of the disease. Early detection is finding cancer at an early stage, when it is less likely to have spread and is easier to treat. Tumor markers were first developed to test for cancer in people without symptoms, but very few markers have been shown to be helpful in this way.
A perfect tumor marker could be used as a cancer screening blood test for all people. The tumor marker would only be found in people with cancer. It would tell doctors the type of cancer, how much cancer there is, and which treatment would work best. At this time there are no tumor marker tests that work like this.
Today, the most widely used tumor marker is the prostate-specific antigen (PSA) blood test. The PSA test is used to screen men for prostate cancer. People with prostate cancer usually have high PSA levels. But it's not always clear what the test results mean -- high PSA levels can be seen in men without cancer, and a normal PSA does not mean that no cancer is present. At this time, not all doctors agree that PSA screening is right for all men.
So far, no other tumor marker has been shown to help screen for cancer in the general population. A few of the markers that are now available can help find cancer at an early stage when only patients at high risk are tested.
Diagnosing cancer
Tumor markers are usually not used to diagnose cancer. In most cases, cancer can only be diagnosed by a biopsy (taking out some tumor cells so they can be looked at under a microscope). Still, markers can help figure out if a cancer is likely. And if a cancer is already widespread when it is found,, tumor markers can help figure out where it started.
An example is a woman who has cancer throughout her pelvis and belly (abdomen). A high level of the tumor marker CA 125 will strongly suggest ovarian cancer, even if surgery can't identify the source. This can be important because treatment can then be aimed at this type of cancer.
Alpha fetoprotein (AFP) is an example of a tumor marker that's used to diagnose cancer. This tumor marker can sometimes be used to help diagnose liver cancer. The level of AFP can go up with some liver diseases, but when it reaches a certain high level in someone with a liver tumor, doctors can be sure that liver cancer is present (even without a biopsy).