CEA Test

Carcinoembryonic antigen (CEA) is a type of glycoprotein, a molecule made of protein and sugar, that plays an important role in how cells stick together during development. It is normally produced by tissues in a developing fetus, especially in the digestive tract. After birth, CEA production is turned off in most healthy tissues, so adults usually have very low levels of it in their blood.

However, CEA levels can become elevated when certain cancers develop. This happens because some cancer cells “reactivate” fetal genes, causing them to start producing CEA again. CEA is most commonly associated with colorectal cancer, but it can also be elevated in breast, lung, pancreatic, thyroid (medullary type), and ovarian cancers. Besides cancer, some benign conditions like smoking, liver disease, and inflammatory bowel disease can also cause mild CEA elevations, making it a nonspecific marker.

Biologically, CEA belongs to a larger group called the CEA-related cell adhesion molecules (CEACAMs). These molecules are involved in how cells stick together, how they grow, and how they migrate. In cancers, CEA may contribute to tumor growth by helping cancer cells avoid dying naturally (a process called apoptosis).

High CEA levels can suggest:

• Advanced or metastatic cancers, especially colorectal cancer
• Residual or recurrent cancer after surgery
• Poor prognosis if levels stay high or increase over time

Low CEA levels are normal but do not completely rule out the presence of cancer, especially in early stages.

Because CEA is not perfectly specific or sensitive, it is not used to screen the general population for cancer. Instead, it is most valuable for monitoring cancer after diagnosis, especially tracking whether cancer has come back after treatment or surgery. For example, in colorectal cancer, CEA levels are usually checked every 3 months during the first 2 years after surgery because early detection of recurrence can lead to better treatment outcomes.

Several important factors can affect CEA readings:

• Smoking can falsely raise CEA levels, even without cancer.
• Liver dysfunction can reduce the body’s ability to clear CEA, leading to higher blood levels.
• Interference from antibodies (such as human anti-mouse antibodies after certain therapies) can make readings inaccurate.
• Differences in laboratory techniques can cause small variations in CEA results.

In short, CEA is best used alongside other tools, like imaging (CT scans) and clinical exams, rather than being relied upon alone. When interpreted carefully, especially in people already diagnosed with cancer, CEA can provide critical information about treatment success, cancer progression, or recurrence.