Tumor markers are substances that can often be detected in higher-than-normal amounts in the blood, urine, or body tissues of some patients with certain types of cancer. Tumor markers are produced either by the tumor itself or by the body in response to the presence of cancer or certain benign conditions. This fact sheet describes some tumor markers found in the blood.
Measurements of tumor marker levels can be useful—when used along with x-rays or other tests—in the detection and diagnosis of some types of cancer. However, measurements of tumor marker levels alone are not sufficient to diagnose cancer for the following reasons:
- Tumor marker levels can be elevated in people with benign conditions.
- Tumor marker levels are not elevated in every person with cancer—especially in the early stages of the disease.
- Many tumor markers are not specific to a particular type of cancer; the level of a tumor marker can be raised by more than one type of cancer.
In addition to their role in cancer diagnosis, some tumor marker levels are measured before treatment to help doctors plan appropriate therapy. In some types of cancer, tumor marker levels reflect the extent of the disease and can be useful in predicting how well the disease will respond to treatment. Tumor marker levels may also be measured during treatment to monitor a patient's response to treatment. A decrease or return to normal in the level of a tumor marker may indicate that the cancer has responded favorably to therapy. If the tumor marker level rises, it may indicate that the cancer is growing. Finally, measurements of tumor marker levels may be used after treatment has ended as a part of follow-up care to check for recurrence.
Currently, the main use of tumor markers is to assess a cancer's response to treatment and to check for recurrence. Scientists continue to study these uses of tumor markers as well as their potential role in the early detection and diagnosis of cancer. The patient's doctor can explain the role of tumor markers in detection, diagnosis, or treatment for that person. Described below are some of the most commonly measured tumor markers.
Prostate-specific antigen is present in low concentrations in the blood of all adult males. It is produced by both normal and abnormal prostate cells. Elevated PSA levels may be found in the blood of men with benign prostate conditions, such as prostatitis and benign prostatic hyperplasia, or with a malignant growth in the prostate. While PSA does not allow doctors to distinguish between benign prostate conditions and cancer, an elevated PSA level may indicate that other tests are necessary to determine whether cancer is present.
PSA levels have been shown to be useful in monitoring the effectiveness of prostate cancer treatment, and in checking for recurrence after treatment has ended. In checking for recurrence, a single test may show a mildly elevated PSA level, which may not be a significant change. Doctors generally look for trends, such as steadily increasing PSA levels in multiple tests over time, rather than focusing on a single elevated result.
Researchers are studying the value of PSA in screening men for prostate cancer. At this time, it is not known whether using PSA to screen for prostate cancer actually saves lives. The National Cancer Institute-supported Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial is designed to show whether the use of certain screening tests can reduce the number of deaths caused by those cancers. For prostate cancer, this trial is looking at the usefulness of regular screening using digital rectal exams and PSA level checks in men ages 55 to 74.
Researchers are also working on new ways to increase the accuracy of PSA tests. Improving the accuracy of PSA tests could help doctors distinguish BPH from prostate cancer, and thereby avoid unnecessary follow-up procedures, including biopsies.
Prostatic Acid Phosphatase
Prostatic acid phosphatase is normally present only in small amounts in the blood, but may be found at higher levels in some patients with prostate cancer, especially if the cancer has spread beyond the prostate. However, blood levels may also be elevated in patients who have certain benign prostate conditions or early stage cancer.
Although PAP was originally found to be produced by the prostate, elevated PAP levels have since been associated with testicular cancer, leukemia, and non-Hodgkin's lymphoma, as well as noncancerous conditions such as Gaucher's disease, Paget's disease, osteoporosis, cirrhosis of the liver, pulmonary embolism, and hyperparathyroidism.
CA 125 is produced by a variety of cells, but particularly by ovarian cancer cells. Studies have shown that many women with ovarian cancer have elevated CA 125 levels. CA 125 is used primarily in the management of treatment for ovarian cancer. In women with ovarian cancer being treated with chemotherapy, a falling CA 125 level generally indicates that the cancer is responding to treatment. Increasing CA 125 levels during or after treatment, on the other hand, may suggest that the cancer is not responding to therapy or that some cancer cells remain in the body. Doctors may also use CA 125 levels to monitor patients for recurrence of ovarian cancer.
Not all women with elevated CA 125 levels have ovarian cancer. CA 125 levels may also be elevated by cancers of the uterus, cervix, pancreas, liver, colon, breast, lung, and digestive tract. Noncancerous conditions that can cause elevated CA 125 levels include endometriosis, pelvic inflammatory disease, peritonitis, pancreatitis, liver disease, and any condition that inflames the pleura. Menstruation and pregnancy can also cause an increase in CA 125.
Carcinoembryonic antigen is normally found in small amounts in the blood of most healthy people, but may become elevated in people who have cancer or some benign conditions. The primary use of CEA is in monitoring colorectal cancer, especially when the disease has spread. CEA is also used after treatment to check for recurrence of colorectal cancer. However, a wide variety of other cancers can produce elevated levels of this tumor marker, including melanoma; lymphoma; and cancers of the breast, lung, pancreas, stomach, cervix, bladder, kidney, thyroid, liver, and ovary.
Elevated CEA levels can also occur in patients with noncancerous conditions, including inflammatory bowel disease, pancreatitis, and liver disease. Tobacco use can also contribute to higher-than-normal levels of CEA.
Alpha-fetoprotein is normally produced by a developing fetus. AFP levels begin to decrease soon after birth and are usually undetectable in the blood of healthy adults. An elevated level of AFP strongly suggests the presence of either primary liver cancer or germ cell cancer of the ovary or testicle. Only rarely do patients with other types of cancer have elevated levels of AFP. Noncancerous conditions that can cause elevated AFP levels include benign liver conditions, such as cirrhosis or hepatitis; ataxia telangiectasia; Wiscott-Aldrich syndrome; and pregnancy.
Human Chorionic Gonadotropin
Human chorionic gonadotropin is normally produced by the placenta during pregnancy. In fact, HCG is sometimes used as a pregnancy test because it increases early within the first trimester. It is also used to screen for choriocarcinoma in women who are at high risk for the disease, and to monitor the treatment of trophoblastic disease. Elevated HCG levels may also indicate the presence of cancers of the testis, ovary, liver, stomach, pancreas, and lung. Pregnancy and marijuana use can also cause elevated HCG levels.
Initially found in colorectal cancer patients, CA 19–9 has also been identified in patients with pancreatic, stomach, and bile duct cancer. Researchers have discovered that, in those who have pancreatic cancer, higher levels of CA 19–9 tend to be associated with more advanced disease. Noncancerous conditions that may elevate CA 19–9 levels include gallstones, pancreatitis, cirrhosis of the liver, and cholecystitis.
CA 15–3 levels are most useful in following the course of treatment in women diagnosed with breast cancer, especially advanced breast cancer. CA 15–3 levels are rarely elevated in women with early stage breast cancer.
Cancers of the ovary, lung, and prostate may also raise CA 15–3 levels. Elevated levels of CA 15–3 may be associated with noncancerous conditions, such as benign breast or ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis. Pregnancy and lactation can also cause CA 15–3 levels to rise.
Similar to the CA 15–3 antigen, CA 27–29 is found in the blood of most breast cancer patients. CA 27–29 levels may be used in conjunction with other procedures to check for recurrence in women previously treated for stage II and stage III breast cancer.
CA 27–29 levels can also be elevated by cancers of the colon, stomach, kidney, lung, ovary, pancreas, uterus, and liver. First trimester pregnancy, endometriosis, ovarian cysts, benign breast disease, kidney disease, and liver disease are noncancerous conditions that can also elevate CA 27–29 levels.
Lactate dehydrogenase is a protein found throughout the body. Nearly every type of cancer, as well as many other diseases, can cause LDH levels to be elevated. Therefore, this marker cannot be used to diagnose a particular type of cancer.
LDH levels can be used to monitor treatment of some cancers, including testicular cancer, Ewing's sarcoma, non-Hodgkin's lymphoma, and some types of leukemia. Elevated LDH levels can be caused by a number of noncancerous conditions, including heart failure, hypothyroidism, anemia, and lung or liver disease.
Neuron-specific enolase has been detected in patients with neuroblastoma; small cell lung cancer; Wilms' tumor; melanoma; and cancers of the thyroid, kidney, testicle, and pancreas. However, studies of NSE as a tumor marker have concentrated primarily on patients with neuroblastoma and small cell lung cancer. Measurement of NSE level in patients with these two diseases can provide information about the extent of the disease and the patient's prognosis, as well as about the patient's response to treatment.