A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. A biomarker may be used to see how well the body responds to a treatment for a disease or condition. 

High biomarker levels can be a sign of cancer. Along with other tests, biomarker tests can help doctors diagnose cancer and plan treatment. Biomarkers are most commonly used to do the following:


  • Guide treatment decisions. Some tumor markers help doctors decide whether to add chemotherapy or immunotherapy after surgery and/or radiation therapy. Other biomarkers help doctors choose which drug(s) or drug combination will work best.


  • Monitor treatment. Doctors may use changes in biomarkers to assess how well treatment is working.


  • Predict the chance of recovery. Biomarkers can help the doctor predict cancer's behavior and response to treatment. They can also predict a person’s chance of recovery.


  • Predict or watch for recurrence. Biomarkers may be used to predict how likely it is that cancer will come back after treatment. Looking for changes in the amount of a biomarker may be part of a patient’s follow-up care plan. It may also help detect a recurrence sooner than other tests.


Biomarker tests may also be used to screen for cancer in people with a high risk of the disease. Some may be done to learn more about cancer when it is first diagnosed. However, the presence or amount of a biomarker alone is not enough to diagnose cancer.


How are tumor markers measured? 


A doctor takes a sample of tumor tissue or bodily fluid and sends it to a laboratory, where various methods are used to measure the level of the biomarker.

If the biomarker is being used to determine whether treatment is working or whether there is a recurrence, the marker’s level will be measured in multiple samples taken over time. Usually, these “serial measurements,” which show whether the level of a marker is increasing, staying the same, or decreasing, are more meaningful than a single measurement.


Does the National Cancer Insitute have guidelines for the use of tumor markers? 


The National Cancer Institute does not have such guidelines. However, some national and international organizations do have guidelines for the use of biomarkers for some types of cancer:


  • The American Society of Clinical Oncology (ASCO) has published clinical practice guidelines on a variety of topics, including biomarkers for breast cancer, colorectal cancer, lung cancer, and others.



What tumor markers are currently being used, and for which colorectal cancer?


A number of biomarkers are currently being used for a wide range of cancer types. Although most of these can be tested in laboratories that meet standards set by the Clinical Laboratory Improvement Amendments, some cannot be and may, therefore, be considered experimental.


Biomarkers that are currently in common use for colorectal cancer are listed below.

BRAF V600 mutations


  • Tissue analyzed: Tumor

  • How used: To select patients who are most likely to benefit from treatment with certain targeted therapies


Carcinoembryonic antigen (CEA)


  • Tissue analyzed: Blood

  • How used: To keep track of how well cancer treatments are working or check if cancer has come back


Circulating tumor cells of epithelial origin (CELLSEARCH®)


  • Tissue analyzed: Blood

  • How used: To inform clinical decision making, and to assess prognosis


KRAS gene mutation analysis


  • Tissue analyzed: Tumor

  • How used: To determine whether treatment with a particular type of targeted therapy is appropriate


Can tumor markers be used in cancer screening? 


Because biomarkers can be used to assess the response of a tumor to treatment and for prognosis, researchers have hoped that they might also be useful in screening tests that aim to detect cancer early, before there are any symptoms. For a screening test to be useful, it should have very high sensitivity (ability to correctly identify people who have the disease) and specificity (ability to correctly identify people who do nothave the disease). If a test is highly sensitive, it will identify most people with the disease—that is, it will result in very few false-negative results. If a test is highly specific, only a small number of people will test positive for the disease who do not have it—in other words, it will result in very few false-positive results.


Although biomarkers are extremely useful in determining whether a tumor is responding to treatment or assessing whether it has recurred, no biomarker identified to date is sufficiently sensitive or specific to be used on its own to screen for cancer.


What kind of research is under way to develop more accurate tumor markers? 


Cancer researchers are turning to proteomics (the study of protein structure, function, and patterns of expression) in hopes of developing new biomarkers that can be used to identify the disease in its early stages, to predict the effectiveness of treatment, or to predict the chance of cancer recurrence after treatment has ended.


Scientists are also evaluating patterns of gene expression for their ability to help determine a patient’s prognosis or response to therapy. 


SOURCE: National Cancer Institute. Used With Permission.