Cancer Antigen 15-3

What Is CA 15-3?

Cancer antigen 15-3 (CA 15-3) is delivered into the bloodstream by active cancer cells. This protein is one of several tumor markers that indicate malignancies (active and dangerous cancers).

CA 15-3 is a mucin, a product of the epitope of Mucin 1 transmembrane glycoprotein (MUC1) gene. Mucins like CA 15-3 function to catalyze an immune response in the presence of pathogens by connecting with an immune antibody.

Together with elevated levels of carcinoembryonic antigen (CEA), high CA 15-3 levels indicate a high probability of cancer, especially breast cancer, a major killer of women across the world. Other markers to check for this type of cancer and to develop a prognosis for recovery include:

• tumor size
• lymph node status
• histological grading
• hormone receptor status

Why Is the CA 15-3 Test Ordered?

CA 15-3 is used in oncology (cancer medicine) for the:

• Detection of primary cancers
• Monitoring of disease progression in cancer patients
• Screening for breast cancer recurrence in patients who have previously been diagnosed

In many cases when tumor regression has been achieved, vigilant monitoring is required because the likelihood of a return of the cancer is high

• Early detection of metastases (secondary developments of cancer cells in nearby tissues or organs)

Levels of CA 15-3 not only can determine the presence of a tumor, but also can aid in assessing the stage of cancer – an important indicator of the chances for a full recovery in breast cancer patients and others.

Who Might Benefit From a CA 15-3 Test?

The American Society of Clinical Oncology recommends a CA 15-3 blood test for anyone with a suspected case of cancer and as a routine screening tool in at-risk patients. Also, because metastases are common in many types of cancer, patients currently receiving cancer treatments are good candidates to receive a CA 15-3 test. In these individuals, a CA 15-3 test can help monitor other organs or tissues to catch any secondary cancers early in development.

If a CA 15-3 test shows concerning results, the next step in the diagnostic process often calls for an analysis of a tissue sampled called a biopsy.

How Is the CA 15-3 Test Performed?

The steps to determine circulating levels of serum CA 15-3 are as follows:

• Draw a blood sample (usually from an arm vein)
• Submit the sample for a laboratory test
• The lab performs an immunoassay to determine CA 15-3 content of the sample
• The lab reports findings of the assay within 1-3 business days

There is no preparation needed on the part of the patient. It's important to keep in mind, though, that some supplements and medications may negatively affect the accuracy of a CA 15-3 blood test. These include:

• The common B-vitamin biotin
• Afinitor (everolimus)

What Health Conditions Do Elevated Levels of CA 15-3 Indicate?

The normal reference range for CA 15-3 is less than 30 U/mL.

High levels of CA 15-3, often seen in combination with elevated levels of carcinoembryonic antigen (CEA), may indicate several types of new cancer or a reversal of progress in treating existing cancers such as:

• Pancreatic cancer (affecting the pancreas)
• Ovarian cancer (affecting one ovary or both ovaries in women)
• Gastric cancer (affecting the stomach)
• Lung cancer (affecting one or both lungs)
• Colon cancer (affecting the colon)
• Uterine cancer (affecting the uterus in women)
• Prostate cancer (affecting the prostate in men)
• Breast cancer (affecting one or both breasts)*

*A particular concern for individuals with extremely high levels of CA 15-3 is metastatic breast cancer, in which the cancer has spread to other areas of the body (called metastases). In these instances, aggressive intervention and frequent follow-up are needed.

Occasionally, elevated CA 15-3 levels might indicate non-cancerous conditions such as:

• Benign liver disease
• Benign breast disease
• Cirrhosis
• Lupus
• Endometriosis
• Hepatitis C

Where Can I Get a CA 15-3 Test Near Me?

Please use our Lab Locator to find a nearby testing station. We will provide the appropriate CPT code as needed.

Due to COVID-19 restrictions, some labs may require special protocols such as social distancing. For routine lab work, we offer many at-home test kits for your home clinical chemistry needs as alternatives to visiting a healthcare provider in-person.

Sources

"Clinical use of biomarkers in breast cancer: Updated guidelines from the European Group on Tumor Markers (EGTM)." Duffy MJ, European Journal of Cancer. https://pubmed.ncbi.nlm.nih.gov/28259011/
"CA 15-3: Reference Range, Interpretation, and Collection." Medscape. https://emedicine.medscape.com/article/2087491-overview
"Serum CEA and CA 15-3 as prognostic factors in primary breast cancer." British Journal of Cancer. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2375330/
"CA 15-3 serum levels in ovarian cancer." Journal of Oncology. https://pubmed.ncbi.nlm.nih.gov/3163419/
"CA 15-3 is present as a novel tumor marker in the sera of patients with breast cancer and other malignancies." Gan To Kagaku Ryoho. https://pubmed.ncbi.nlm.nih.gov/3865634/
"Serum CA 15-3 assay in the diagnosis and follow-up of breast cancer." British Journal of Cancer." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2246767/

Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: Feb 28, 2022