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.

These tests are most often done on people already 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.