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 other tissue. 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 a sample 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 cancer may 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 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 called “What’s new in tumor marker research?”