What is Carcinoembryonic Antigen (CEA)?

Carcinoembryonic antigen (CEA) is a protein made by gastrointestinal cells. It is mostly made during fetal development (in the womb, before birth), and healthy adult levels are very low. CEA level is often increased in colorectal cancer (bowel cancer) and is considered a tumor marker of colon cancer and rectal cancer. CEA is secreted by colorectal adenocarcinoma cells and measured in the blood.

High CEA level may also be found in patients with some benign (non-cancer) digestive system diseases, like advanced liver disease, pancreatitis, or ulcerative colitis. People who smoke cigarettes may also have increased CEA that is not due to cancer. CEA can be increased in patients with other types of cancer, including breast cancer, lung cancer, and thyroid carcinoma. CEA is not always increased in colorectal cancer, more than 10% of patients with CRC may have normal CEA level.

CEA level is a prognostic biomarker. It gives information about the likely outcome of disease. CEA is also a predictive biomarker. CEA level is a predictor of whether you might benefit from adjuvant chemotherapy after surgery in stage II colorectal cancer (CRC).  

How is CEA tested?

CEA is measured in a blood sample. CEA is usually tested at multiple timepoints, such as before, during, and after cancer treatment. This allows comparison of CEA levels over time. While the actual level of CEA in the blood is an important measure, tracking the trend of increasing or decreasing CEA over time provides even more useful information. A carcinoembryonic antigen test may also be called a CEA test, CEA blood test, or CEA assay.  

How are CEA biomarker test results reported?

CEA is reported as a number, representing the amount of CEA found in a specific amount of blood. Normal levels are usually less than 3 ng/ml (nanograms per milliliter), though the exact normal cut-off number varies a little bit between laboratories. Heavy smoking can cause levels as high as 5 ng/ml. CEA level may also be normal in colorectal cancer.  

What do my CEA results mean for me? How do my CEA results impact my colorectal cancer treatment?

If you have a high CEA level

• Increased CEA may help confirm the presence of cancer during diagnosis.
• Elevated CEA level alone, without cancer symptoms or findings, is not enough to diagnose colorectal cancer.
• Higher CEA level is associated with poorer overall survival rate in colorectal cancer.
• Generally, CEA level increases with increasing cancer stage (from stage I to stage IV / metastatic disease), but this is not true in every patient. Patients with advanced or metastatic colorectal cancer (mCRC) tend to have the highest CEA levels.
• If you have stage II colorectal cancer and a high CEA level, you may benefit from adjuvant chemotherapy in addition to colon and/or rectum surgery. Adjuvant therapy is a treatment given after the main (primary) treatment to kill any remaining cancer cells.  

If your CEA increases over time

• Increasing CEA level during treatment may be caused by cancer progression (tumor growth or metastasis). If your cancer is progressing, your oncology team will adjust your treatment plan.
• CEA level may increase after starting chemotherapy for colorectal cancer, and then decrease as treatment continues. This is called a “CEA flare”. Patients who experience a CEA flare have a better prognosis than those who do not have a CEA flare.  
• Increasing CEA level after successful treatment may be caused by cancer recurrence. If your CEA level increases during follow-up monitoring after treatment, your healthcare team will do more testing (such as colonoscopy, biopsy, or PET/CT scan) to confirm or rule out a recurrence.
• Treatment options for colorectal cancer recurrence are based on many factors, including your response to previous treatments and the results of other biomarker testing.

If your CEA decreases over time

• Decreasing CEA is a sign that your colorectal cancer treatment is working.
• CEA levels usually decrease after successful colorectal cancer surgery.

If your CEA is normal

• Normal CEA level does not rule out the possibility of cancer because some colorectal cancers do not cause increased CEA level.
• Normal CEA is associated with a better overall survival rate in colorectal cancer.

Who should be tested for CEA?

CEA should be tested in all colorectal cancer patients before treatment begins. This lets your healthcare provider compare CEA levels before, during, and after cancer treatment. If you have not had a CEA level test, or are not sure if you have had one, please talk to your healthcare team. CEA level can be a useful biomarker at any cancer stage, and at any point in your cancer treatment.