Tumor markers blood tests
In previous posts, we discussed cancer screening tests and cancer hereditary tests. Cancer screening tests are used if cancer is suspected because of symptoms or family history with the goal to identify cancer early. Hereditary cancer tests are used to identify genetic risk and susceptibility to certain cancers. The third category discussed in this post is tumor markers blood tests. During treatment, or after apparently successful treatment, active monitoring is often recommended to identify if the cancer is responding to treatment or has returned or spread before any symptoms appear. Monitoring may include increased surveillance or routine blood tests for tumor markers, and increasingly, molecular genetic tests. There are hundreds of genes that can be relevant and dozens of unique tests based on DNA Circulating Tumor DNA. This post will not cover these tests as all of them required prescribing physicians and are associated with certain therapeutics.
What are tumor marker blood tests?
Tumor markers are molecules in our body that are produced in much higher quantities when certain cancers present. These substances may be found in the blood, urine, stool, or tumor tissue. Most of these substances are proteins or complex carbohydrates (glycans). Because an elevated tumor marker doesn’t necessarily indicate cancer e.g. these tumor marker blood tests are not specific only to cancer, tumor markers cannot be used alone to diagnose cancer but are used in combination with other tests, such as biopsies to monitor the overall effectiveness of cancer treatment.
Over the past decades, cancer markers blood tests, mainly carbohydrate antigens have served as important tumor markers and as the targets of anti-cancer drugs. For example, carbohydrate antigen 125 (CA-125) shows the function in advancing tumorigenesis and tumor proliferation by several different mechanisms; carbohydrate antigen 19-9 (CA 19-9) is the tumor marker in the management of pancreatic cancer; carbohydrate antigen 15-3 (CA 15-3) is a tumor marker for many types of cancer, especially breast cancer; carbohydrate antigen 72-4 (CA 72-4) is a tumor marker found to be elevated in a variety of human adenocarcinomas, particularly in gastric cancer.
CA 125 test
A CA 125 test measures the amount of the carbohydrate antigen 125 (CA-125) in a person’s blood. CA-125 is a glycoprotein that is a biomarker or tumor marker. The protein is found in higher concentrations in cancer cells, particularly ovarian cancer cells. Cancer types that may cause higher-than-normal levels of CA-125 are a long list that includes Ovarian, Endometrial, Fallopian tube, Pancreatic, Stomach, Esophageal, Colon, Liver, Breast, and Lung. Cancer that has spread to the peritoneum, the abdomen’s lining, may also cause higher-than-normal levels of CA-125. It’s important to note that conditions other than cancer may cause higher levels of CA-125, including uterine fibroids, endometriosis, lupus, liver disease, and pancreatitis.
CA 15-3 test
Cancer Antigen CA 15-3 is delivered into the bloodstream by active cancer cells. CA 15-3 test is one of several tumor markers that indicate malignancies (active and dangerous cancers). CA 15-3 is a which are high molecular weight, heavily glycosylated protein (glycoconjugates) produced by epithelial tissues. Together with elevated levels of carcinoembryonic antigen (CEA), high CA 15-3 levels indicate a high probability of cancer, especially breast cancer. This test may be useful for monitoring patients with metastatic breast cancer and certain ovarian cancers. The CA 15-3 values from sequential samples have a high correlation with the clinical course in most patients with metastatic breast cancer.
CA 27.29 test
Cancer antigen 27.29 is a highly polymorphic glycoprotein belonging to the mucin family and is the product of the muc-1 gene. CA 27.29 test is most useful to use serial measurements of this test to monitor both the course of disease and response to therapy. A reduction in levels of this test indicates a good response to treatment while increasing levels indicate resistance to therapy. An elevated serum CA 27.29 level in patients in remission of stage II or III breast cancer provided a high likelihood of recurrent disease -- Doctors describe recurrent cancer by where it develops and how far it has spread.
CA 19-9 test
Carbohydrate antigen 19-9, also known as sialyl-Lewisᴬ, is a tetrasaccharide that is usually attached to O-glycans on the surface of cells. It is known to play a role in cell-to-cell recognition processes. It is also a tumor marker used primarily in the management of pancreatic cancer but a large percentage of patients with gastrointestinal tumors (such as pancreatic, liver, gastric, and colorectal tumors) and some other malignancies have been shown to have elevated serum CA 19-9 levels. Therefore, CA 19-9 test can be useful for monitoring pancreatic cancer disease activity or predicting relapse following treatment but not for diagnosis. Three percent to 7% of the population do not have the gene to express the CA 19-9 and therefore will be unable to produce the CA 19-9 antigen even in the presence of malignant tissue.
Chromogranin A (CGA) test
CGA test measures levels of Chromogranin A in the blood. Chromogranin A is a protein produced by cells found in endocrine glands throughout the body. Certain types of tumors caused increased production of Chromogranin A. Carcinoid tumors, which typically form in the lungs or gastrointestinal tract are often associated with increased CGA levels. Measuring CGA levels can aid in diagnosing some types of cancer as well as monitoring response to treatment. A Chromogranin A test is often ordered when a person is experiencing symptoms such as rapid heart rate, nausea, diarrhea, wheezing, coughing, difficulty breathing, or flushing of the face which are associated with carcinoid tumors. The CGA test may also be ordered to see how well a person is responding to treatment or to check for the recurrence of tumors.
Carcinoembryonic antigen (CEA) test
Carcinoembryonic antigen is a protein found in the developing tissues of a fetus. It drops to a very low level by the time a baby is delivered. CEA is generally seen in extremely low amounts in the blood of people, but it can be raised in cancer patients. CEA test examines the quantity of CEA in the blood to aid in the evaluation of cancer patients.
CEA is a tumor indicator. CEA was once assumed to be a particular marker for colon cancer, however, subsequent research has revealed that an elevation in CEA can be detected in a variety of malignancies. Non-cancer disorders such as inflammation, cirrhosis, peptic ulcer, ulcerative colitis, rectal polyps, emphysema, and benign breast disease, as well as smokers, can cause an increase in CEA. As a result, it is ineffective as a general cancer screening tool, although it does play a role in assessing cancer therapy response. An initial CEA baseline test may be performed after a person has been diagnosed with cancer. If this level is raised, serial CEA testing may be used to track cancer's progress as the patient receives treatment.
Tumor markers blood tests are useful tools to monitor progression, malignancy, treatment response, and recurrence in various cancers. Due to lack of specificity (elevate in several types of cancers and other diseases) these tests are not used for screening or diagnosis of cancer disease but are good for disease management.