How Do Tumor Markers Work?
When diagnosing cancer, blood and pieces of tumor tissue are tested. These tests help to determine the characteristics of the tumor (aggressiveness, rate of growth, and degree of abnormality). Tests for tumor markers may be used with other laboratory tests or procedures such as x-rays to detect and diagnose some cancers.
Tumor markers may be proteins, antigens, or hormones. Tumor marker tests are not used by themselves for making a cancer diagnosis because most markers can be found in elevated levels in people who have benign conditions, and because no tumor marker is specific to a particular cancer.
How tumor markers are measured
Tumor markers are most often measured in blood and urine. They can also be found in tumors and other tissues.
Tumor markers are sent to a laboratory where various methods are used to measure the levels. The marker is usually found by combining the sample with man-made antibodies that react with the tumor marker protein.
Are tumor markers reliable indicators of cancer?
Not every tumor will cause an elevation in the tumor marker test, especially in the early stages of cancer. Physicians can use changes in tumor marker levels to follow the course of the disease, to measure the effect of treatment, and to check for recurrence.
Tumor markers are not always reliable for the following reasons:
- Most tumor markers can be made by normal cells, as well as cancer cells.
- Tumor markers can be associated with noncancerous conditions.
- Tumor markers are not always present in early stage cancers.
- People with cancer may never have elevated tumor markers.
- Even when tumor marker levels are high, they are not specific enough.
