Breast cancer tumor markers are substances, usually proteins or hormones, that are produced by the body in reaction to a tumor or by the tumor itself. They are found in the blood, urine or tissues or in the tumor tissue. Different markers indicate different stages of tumor progression and tumor growth, and they can be used to guide diagnosis and treatment and to predict prognosis.
The first stage of breast cancer detection is the mammogram, ultrasound or breast magnetic resonance imaging (MRI) exam, all of which are sensitive enough to detect breast cancer before any symptoms are noticeable. If there are any suspicious signs, then a biopsy is carried out, and only then are tests for breast cancer tumor markers given. The tests are not sufficient by themselves, because the proteins and hormones that they detect are sometimes produced in the body by other conditions.
Before breast cancer treatment begins, a tumor marker test is given in order to establish baseline levels with which to compare later results. Although not tumor marker tests as such, estrogen receptors and progesterone receptors are measured to establish the type of cancer. Then the presence of human epidural growth factor 2 is determined, because this is a protein that is present in nearly half of patients who have breast cancer.
In order to establish the type of breast cancer tumor and the best possible course of treatment, the first marker test is likely to be the urokinase plasminogen activator and plasminogen activator inhibitor test. Urikinase is an enzyme that is present in the blood plasma and urine produced normally by the kidneys but also can be be produced by tumors. This is a prognostic test, because high levels of urokinase plasminogen activator and plasminogen activator inhibitor usually mean that the cancer has become more aggressive.
Testing for breast cancer tumor markers depends on the different stages of the cancer. Some breast cancer tumor markers, such as carcinoembryonic antigen, cancer antigen 27.29 and cancer antigen 15-3, are indicative of breast cancer that has metastasized. Oncotype DX is a genetic test that helps to determine the likelihood of the breast cancer recurring. The ki-67 leveling index is another indication of how quickly the cancer cells are proliferating and thus how aggressive the cancer is. This tumor marker test measures the activity of the antigen ki-67, a nuclear protein that is present during active cellular phases but absent in resting cells.
A decrease in tumor marker levels compared to the baseline is a good indication that the cancer is responding to treatment, and an increase in levels usually means that the therapy needs to be changed. At the end of a treatment phase or during any follow-up treatments, tests for breast cancer tumor markers might be required to monitor any recurrence. Follow-up visits after four to six months are recommended.