These tests look for tumor markers, sometimes called cancer markers, in the blood, urine, or body tissues. Tumor markers are substances made by cancer cells or by normal cells in response to cancer in the body. Some tumor markers are specific to one type of cancer. Others can be found in several types of cancers.

Because tumor markers can also show up in certain noncancerous conditions, tumor marker tests are not usually used to diagnose cancer or screen people at low risk of the disease. These tests are most often done on people who have already been diagnosed with cancer. Tumor markers can help find out if your cancer has spread, whether your treatment is working, or if your cancer has come back after you’ve finished treatment.