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Breast cancer markers
Medical expert of the article
Last reviewed: 04.07.2025
Analysis of breast tumor markers - an immunochemical blood test - is carried out during the diagnosis and treatment of tumors of the mammary glands along with such diagnostic procedures as mammography, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI).
A correct diagnosis can be made and appropriate treatment prescribed only on the basis of a combination of hardware examination data and a blood test for tumor markers.
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Breast cancer tumor markers: CA 15-3
Mutated cancer cells synthesize a protein (high-molecular glycoprotein with O-linked oligosaccharide chains), which the body perceives as an antigen - a foreign element. This cancer antigen (CA) penetrates the blood and lymphatic vessels and circulates with the blood and lymph flow. That is, in the presence of a malignant tumor disease, CA can be detected using a blood test.
Tumor markers of breast cancer have been identified - cancer antigen 15-3 (CA 15-3) and cancer antigen 27-29 (CA 27-29). Domestic oncologists classify CA 15-3 as a specific cancer antigen in primary malignant tumors of the mammary glands, although it is known that CA 15-3 is also elevated in the blood serum in cancer of the lungs, colon, pancreas, liver, ovaries, cervix and endometrium.
Doctors prescribe a test for breast tumor markers not only to differentiate breast cancer from benign neoplasms, but also to monitor the progress of an already diagnosed pathology, evaluate the effectiveness of the therapy, and to detect cancer metastases.
To determine the cancer antigen, blood is taken from a vein (on an empty stomach, no earlier than 8 hours after the last meal) and subjected to immunochemical testing. The norm for breast tumor markers CA 15-3 is up to 26.9 U/ml, in foreign clinics the upper limit of the normal range is 30 U/ml.
Breast cancer tumor markers: CA 27.29
The American Society of Clinical Oncology (ASCO) considers the breast tumor marker test CA 27-29 to be the only blood test that is specific for breast cancer.
The CA 27-29 test measures the serum level of the soluble form of the glycoprotein MUC1, which is expressed on the membranes of most breast carcinoma cells. The norm for breast tumor markers CA 27-29 is a level of less than 38-40 U/ml.
The sensitivity of this tumor marker, according to experts, is also not high enough: the result is higher than normal in cases of endometriosis, ovarian cysts, in the first trimester of pregnancy, and in cases of benign diseases of the mammary gland, kidneys, and liver.
Breast cancer tumor markers: CEA
Abroad, patients with breast pathologies undergo another test - a test for carcinoembryonic antigen (CEA). In domestic clinical practice, it is called the oncomarker CEA - cancer-embryonic antigen.
Oncologists claim that to make a correct diagnosis, it is necessary to combine the determination of the breast cancer tumor marker CA 15-3 with the detection of CEA, the cancer-embryonic antigen, in the blood. This antigen practically disappears after birth, and it is difficult to detect it in the blood serum of healthy adults. The norm for the CEA tumor marker is up to 5 ng/ml.
But in cancer diseases (especially in rectal, lung, breast, ovarian, pancreatic, prostate cancer and metastases to the liver and bone tissue), the carcinoembryonic antigen increases to 20 ng/ml and more. Moreover, more than a third of patients diagnosed with breast cancer have elevated CEA levels in their blood.
However, an increase in CEA (within the range of less than 10 ng/ml) can also be observed in some diseases of the gastrointestinal tract, liver or lungs that are not associated with oncology.
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Breast Cancer Tumor Markers: HER2
Another analysis – for the human epidermal growth factor receptor (HER2, Human Epidermal Growth Factor Receptor 2) – provides information about the presence of tyrosine protein kinase – a protein of transmembrane cellular receptors that accelerate the growth and division of epithelial cells.
For analysis, a tumor biopsy is performed or a tissue sample is taken after surgery to remove the tumor. According to statistics, this protein is present in large quantities in 25-30% of breast cancer cases. The HER2 level is also elevated in malignant diseases of the uterus, ovaries and stomach.
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Decoding breast tumor markers
It should be noted that, according to research data, breast tumor markers, in particular CA 15-3, are elevated in approximately 20% of patients with breast cancer diagnosed at the first or second stage of the disease. Although at later stages, breast tumor markers are elevated in eight out of every ten patients.
Cancer antigen 15-3 (CA 15-3), cancer antigen 27-29 (CA 27-29), and carcinoembryonic antigen (CEA) are detected in 50-90% of women with metastatic breast cancer when decoding breast tumor markers.
Despite the radiological signs of disease persistence, the decoding of breast tumor markers CA 15-3 may show an absolutely normal level (that is, within 30 U/ml), and this means that the treatment was successful, and the residual tumor recorded on the mammogram is no longer viable.
If breast tumor markers are elevated - CA 15-3 above 30 U/ml, CA 27-29 above 40 U/ml - then there are good reasons to diagnose oncology. When the indicators do not decrease after treatment, there are two options: either the treatment was incorrect, or the disease is progressing.
If breast tumor markers increase after therapy, this is a clear sign of its ineffectiveness. In this case, the absence or presence of clinical improvements is taken into account.
Thus, decoding breast cancer markers, such as the cancer antigen, helps to identify relapses of breast cancer after treatment, as well as metastases at earlier stages.
HER2 breast tumor markers show whether a drug such as Trastuzumab (Herceptin, Kadcyla), which blocks the synthesis of a protein called transmembrane cell receptors and stops the growth of cancer cells, can be used in treatment. In some cases, the results of this biological testing help oncologists assess the tumor's tendency to progress, determine how the body responds to treatment, and determine the need for specific chemotherapy.
By the way, breast tumor markers may be slightly elevated in the last trimester of pregnancy, with liver cirrhosis, chronic hepatitis, systemic lupus erythematosus, sarcoidosis, tuberculosis. Therefore, today, breast tumor markers are not an absolute indicator of oncology without tumor visualization using mammography.