The CEA (Carcinoembryonic Antigen) test is a blood test that measures the level of CEA, a protein that can be produced by certain cancers. CEA is often called a tumor marker because higher-than-expected levels may be associated with some cancers, especially colorectal cancer and other gastrointestinal (GI) cancers. Small amounts of CEA can be present in healthy adults, and levels can also rise for reasons that are not cancer.

In most cases, the CEA test is not used as a stand-alone test to diagnose cancer. Instead, it is mainly used in oncology to monitor cancer treatment and to help detect possible recurrence (return of cancer) after treatment—particularly in people who have already been diagnosed with colorectal cancer or another CEA-producing tumor.

How to understand results (in plain language):

Lower or normal CEA levels are generally reassuring, but they do not completely rule out cancer (some cancers do not make CEA). Higher CEA levels can suggest that a cancer may be present, growing, or returning, but they can also occur due to non-cancer causes such as smoking, inflammation, infection, or certain liver and bowel conditions. Most importantly, doctors often look at the trend over time (rising or falling levels across repeated tests) rather than a single number. A falling CEA during treatment may indicate that therapy is working, while a steadily rising CEA after treatment may prompt further evaluation (such as imaging or colonoscopy) to check for recurrence.

A doctor may order a CEA test for cancer monitoring rather than as an initial screening test. It is commonly used when someone has a known cancer where CEA can be informative, especially colorectal cancer.

Common reasons the CEA test is ordered include:

1) Monitoring response to cancer treatment
If you are receiving cancer treatment (such as surgery, chemotherapy, radiation therapy, targeted therapy, or immunotherapy), CEA can help your care team see whether the tumor marker level is going down, staying the same, or rising. This is often used alongside scans and clinical exams.

2) Checking for recurrence after treatment
After successful treatment—especially after surgery for colorectal cancer—CEA may be measured at regular intervals as part of recurrence monitoring. A rising CEA level may lead to additional testing to look for a return of cancer, sometimes before symptoms appear.

3) Helping evaluate suspected spread (metastasis) or progression
If someone with known cancer develops new symptoms or imaging changes, the CEA test may help assess whether disease activity is increasing. It is not definitive on its own, but it can add useful information.

4) Supporting diagnosis in specific situations (not as a screening test)
In some cases, when cancer is suspected based on symptoms, exam findings, or imaging, CEA may be ordered as part of a broader work-up. However, because CEA can be elevated for non-cancer reasons and can be normal in some cancers, it is not recommended as a general population screening test.

Symptoms or clinical situations that may lead to testing (usually alongside other tests): unexplained weight loss, persistent abdominal pain, changes in bowel habits, blood in the stool, unexplained anemia, persistent fatigue, or abnormal imaging findings—especially in someone with a history of GI cancer.

Important factors that can affect results: Smoking can raise CEA levels. Certain non-cancer conditions—such as liver disease or inflammation in the digestive tract—can also increase CEA. Your clinician will interpret results in the context of your health history, imaging, and other laboratory tests.

• Colorectal cancer (colon cancer and rectal cancer)
• Other gastrointestinal cancers (e.g., gastric/stomach cancer, pancreatic cancer)
• Esophageal cancer
• Lung cancer (some types may produce CEA)
• Breast cancer (CEA may be used in select cases for monitoring)
• Liver disease (e.g., hepatitis or cirrhosis can elevate CEA)
• Inflammatory bowel disease (Crohn’s disease, ulcerative colitis)
• Pancreatitis
• Benign gastrointestinal conditions (e.g., diverticulitis)

• Monitoring treatment effectiveness in colorectal cancer and other CEA-producing tumors
• Recurrence monitoring after cancer surgery or completion of therapy
• Supporting follow-up care plans in oncology (tracking tumor marker trends over time)
• Helping guide decisions about additional testing (such as imaging or colonoscopy) when CEA rises
• Establishing a baseline tumor marker level at diagnosis for future comparison during cancer monitoring