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Tumor Markers
What are tumor markers?
Tumor markers are substances that can be found in the body when cancer is present. The classic
tumor marker is a protein that can be found in the blood in higher than normal amounts when a
certain type of cancer is present, but not all tumor markers are like that. Some are found in urine or
other body fluid, and others are found in tumors and othertissue. They may be made by the cancer
cells themselves, or by the body in response to cancer or other conditions. Most tumor markers are
proteins, but some newer markers are genes or other substances.
There are many different tumor markers. Some are linked only to one type of cancer, while others
can be found in many types of cancer.
To test for a tumor marker, the doctor most often sends asample of the patient’s blood or urine to a
lab. Sometimes a piece of the tumor itself is tested for tumor markers.
Tumor markers alone are rarely enough to show that 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 cancermay
have higher levels of a tumor marker.
This is why most doctors use only certain tumor markers. When a doctor looks at the level of a
tumor marker, he or she will consider it along with the patient’s history, 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 certaingenetic 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 called “What’s new in tumor marker research?”

How are tumor markers used?
Tumor markers can be helpful in anumber of ways.

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’s less likely to have spread and is easier to
treat. Tumor markers were first developed to screen for cancer – to look for cancer in people
without symptoms – but very few markers have beenshown to be helpful in this way.
A perfect tumor marker would be one that 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 usedtumor marker is the prostate-specific antigen (PSA) blood test. The
PSA test is used to screen men for prostate cancer. Men 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 always mean that no cancer is present. PSA is not
a perfect tumor marker. And at thistime, not all doctors agree that PSA screening is right for all
men.
Right now, no other tumor marker is used to help screen for cancer in the general population.
Some of the markers used now can help find cancer at an early stage, but they are only checked in
people who are known to be at high risk for certain types of cancer.

Diagnosing cancer
Usually, tumor markers are not used to diagnosecancer. In most cases, cancer can only be
diagnosed by a biopsy. (This means taking out some cells from a tumor so they can be checked for
cancer by looking at the cells under a microscope.) Still, tumor markers can help figure out if
cancer is a possibility. And if a cancer is already widespread when it’s found, tumor markers can
help figure out where it started.
For instance, let’s say a...