Tumor markers are substances that are produced by cancer cells or by other cells in the body when they are in the presence of cancer cells. Tumor markers are usually molecules called proteins. They are generally common substances emitted by cells under normal circumstances, but they can be made at much higher levels in the presence of cancer. In some cases, certain genes may also serve as tumor markers rather than proteins.
What kinds of tumor markers are there?
No single marker can detect all kinds of cancer. That means that different molecules or markers are used to detect or make treatment decisions for different types of cancer.
Using markers to detect cancer is not a perfect science. Some markers can be produced at high levels when patients have diseases or conditions that are unrelated to cancer. For example, the prostate-specific antigen (PSA) test is used to detect prostate cancer. But PSA can be produced at high levels because of other non-serious conditions, such as a urinary tract infection or an enlarged prostate.2
How do you find tumor markers in the body?
Tumor markers generally circulate in the body or they may be found in one or more of your tissues. Doctors or other health care providers can detect them by taking a sample and sending it to a laboratory for testing. Depending on which marker a doctor is looking for, you may be asked to give a sample of your blood, urine, stool, other fluids, tumor tissues, or other tissues to as a first step for detecting tumor markers.1
How are tumor markers used?
In cancer care, tumor markers can be used to detect cancer in the first place as well as to see how well a treatment is working. If you have lower levels of a particular type of tumor marker over time, that generally means treatment is working.1
Tumor markers may also be used to help manage your care. In some cases, researchers have learned that cancers with certain kinds of tumor markers respond best to a particular course of treatment. The presence of tumor markers can also be used to detect if cancer has returned after treatment.
Detecting tumor markers alone may not be enough to diagnose cancer, so doctors often have to conduct a biopsy to test your tissues for signs of cancer, as well. To date, there is no tumor marker that can serve as a reliable early screening test for cancer.
What tumor markers are being used for advanced breast cancer?
In the case of advanced breast cancer, doctors look for1:
CA15-3/CA27.29 in the blood to see how well a treatment is working or if the disease has come back.
Circulating tumor cells of epithelial origin (these are the types of tissues that line the organs and a common origin for breast cancer tumors)3 in the blood to inform treatment decisions and assess prognosis.
Estrogen receptor (ER)/progesterone receptor (PR) on the tumor to determine whether hormone or certain targeted therapies might work.
HER2/neu gene amplification or protein overexpression on the tumor to determine whether certain therapies might work.
Urokinase plasminogen activator (uPA) and plasminogen activator inhibitor (PAI-1) on the tumor to understand how fast-growing the tumor is and to help make treatment decisions.
21-Gene signature on the tumor to assess the risk of the cancer returning.
70-Gene signature on the tumor to assess the risk of the cancer returning.
What research is underway to study tumor markers?
Researchers are turning to a field called proteomics to see if they can find additional useful tumor markers to help them detect cancer and make accurate treatment decisions. Proteomics is the study of protein structure, function, and patterns of expression.
Researchers are also looking at patterns of gene expression to help them determine how likely it is for different cancers to come back. For example, scientists were able to tell that among women with non-metastatic breast cancer displaying particular tumor markers, people with low levels of expression of a series of particular genes (based on 21-gene recurrence scores) did not experience a recurrence when they were given hormone therapy alone. This information enabled them to be spared the toxicity and side effects of chemotherapy while still keeping the risk of recurrence low.1
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Tumor Markers. National Cancer Institute. November 4, 2015. Available at: https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet Accessed June 8, 2019.
Elevated PSA (Prostate-Specific Antigen) Level. The Cleveland Clinic. October 25, 2016. Available at: https://my.clevelandclinic.org/health/diseases/15282-elevated-psa-prostate-specific-antigen-level Accessed June 10, 2019.
Types of Breast Cancer. American Cancer Society. September 25, 2017. Available at:
https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/types-of-breast-cancer.html Accessed June 10, 2019.