Use of Blood Marker Tests for Cancer Treatment
What is advanced breast cancer?
Breast cancer is a disease in which cells in the breast grow out of control. It can develop in different parts of breast tissue. DNA mutations cause changes in breast cells such that they become cancerous. Because these cancerous (malignant) cells multiply rapidly they sometimes break off from the original tumor and spread through the body via the bloodstream or the lymphatic system.
What breaks off from these cancerous tumors are cancer cells and proteins, substances produced by the cancerous cells that circulate in the blood that may be indicative of, or markers for, a specific type of cancer.1 Referred to by different names including blood markers, tumor markers, serum or biomarkers, they are substances that occur at elevated levels in blood urine and tissue of some people with cancer. These circulating tumor cells (CTC) are present in the bloodstream as they separate from the cancerous mass. CTC and proteins can be measured by basic blood tests. Elevated CTC and protein counts may indicate that the presence of cancer, either in a primary location or to other places where cancer has spread.
Biomarker tests can be used for many reasons, including as a screening tool for people who have no indications of cancer. Some available blood markers can aid in the diagnosis of different types of cancer, but this is not a conclusive diagnostic method for breast cancer.2
Blood marker tests
Laboratory analysis of blood tests which can measure proteins and tumor cell activity in the body provides information to oncologists useful in diagnosing and monitoring metastatic breast cancer and other cancers.2 For breast cancer there are multiple tumor markers considered by physicians:
- CA 15.3: is used to identify breast and ovarian cancers
- TRU-QUANT and CA 27.29: may indicate the presence of breast cancer
- CA125: may indicate initial ovarian cancer as well as the recurrence of breast and ovarian cancer
- CEA (carcinoembryonic antigen): is a marker for multiple cancers including colon, lung, and liver. It may also indicate the spread of breast cancer to other areas of the body.
These tests may provide information on the progression of cancer, evaluate whether tumors are responding to treatment, or if there has been a recurrence. Some test results have had success as being predictive of which people may develop a recurrence of their cancer. Breast cancer markers are not considered useful to singularly identify recurrence, to monitor those who are disease-free following early-stage breast cancer, nor have they demonstrated effectiveness in prolonging the lives of people who had early-stage breast cancer and who are now disease-free.2
The U.S. Food and Drug Administration (FDA) has approved the CELLSEARCH® test to monitor circulating tumor cells that have detached from a primary tumor and end up in the bloodstream or lymphatic system of other parts of the body.4 It is a blood test used by oncologists to assess the prognosis of patients with advanced metastatic breast cancer as well as prostate and colorectal cancer.
Like other blood marker tests, the results should be used along with other clinical information gathered from diagnostic imaging and lab tests, a physical exam, and complete medical history.
When to do blood marker tests
The indications for conducting these blood marker tests can be different reasons at different stages.3 Blood marker test results can be used to help diagnose disease, as early indicators of breast cancer progression to other parts of the body, to assess response to treatment or recurrence after treatment. This information can be used by your medical team to make decisions about care and therapeutic options. These tests may be administered periodically to assess any changes in the levels (concentrations) of these blood markers.
What the blood marker test results mean
Blood marker tests are not used in isolation, they are generally considered one evaluation tool in the diagnostic and monitoring process. Some people without cancer have higher than normal levels, someone with cancer could have low levels of tumor markers, and sometimes tests have false positives.2 A negative result alone cannot confirm that breast cancer is gone, and a positive result doesn't mean that the cancer is still growing
Breast cancer blood marker tests currently available have limitations. Marker levels can be elevated due to other conditions.3 These tests help with diagnosis but using cancer marker tests to find metastatic breast cancer hasn't helped improve survival yet.
Imaging tests, including mammogram, MRI, and ultrasound are more conclusive to diagnose and monitor breast cancer. Therefore, blood marker level indications are generally followed by imaging tests to confirm the presence or absence of tumors.
Abnormal blood marker levels can cause concern for patients and their families. You should always discuss with your doctor the test implications and what other diagnostic tools will be considered in as part of your breast cancer care plan.4
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