Carcinoembryonic Antigen (CEA) is a substance produced by the body, measurable in the blood. While present at low concentrations in healthy individuals, elevated CEA levels can indicate certain conditions. It is particularly relevant in colon cancer, offering insights into disease management.
Understanding Carcinoembryonic Antigen (CEA)
Carcinoembryonic antigen is a glycoprotein with carbohydrate chains attached. It functions in cell adhesion. CEA is naturally produced in gastrointestinal tissue during fetal development, largely stopping before birth.
In healthy adults, CEA is present at very low levels. However, certain cancer cells, particularly those from the colon and rectum, can restart CEA production, releasing it into the bloodstream. While most commonly associated with colorectal cancer, elevated CEA levels can also occur with other cancer types, including those of the pancreas, stomach, breast, lung, and ovaries.
Defining Normal CEA Levels
A normal CEA level in the blood is considered quite low. For non-smokers, levels are below 2.5 nanograms per milliliter (ng/mL) or 3 ng/mL. Individuals who smoke may have slightly higher CEA levels, up to 5 ng/mL.
These ranges can vary between different laboratories. A single elevated CEA result does not necessarily indicate cancer, and conversely, a normal CEA level does not rule out cancer. For patients diagnosed with cancer, a baseline CEA level is established before treatment to provide a reference point for future comparisons.
Factors Influencing CEA Levels
Carcinoembryonic antigen levels can be elevated by several factors unrelated to cancer. Smoking is a common cause of increased CEA, with smokers having higher baseline levels compared to non-smokers.
Various non-cancerous medical conditions can also lead to elevated CEA, including inflammatory bowel diseases (Crohn’s disease, ulcerative colitis), pancreatitis, liver conditions such as cirrhosis, emphysema, chronic obstructive pulmonary disease (COPD), peptic ulcers, gallstones, diverticulitis, and benign breast disease. Elevations due to these benign conditions are less than 10 ng/mL.
Role of CEA in Colon Cancer Care
CEA testing is not used for initial screening or diagnosis of colon cancer in the general population. Its sensitivity and specificity are not sufficient for this purpose. Instead, CEA measurements serve specific roles in the management of diagnosed colon cancer.
One application is monitoring the effectiveness of cancer treatment. If CEA levels decrease during therapy, it may suggest the treatment is working. Conversely, stable or rising CEA levels can indicate the cancer is not responding to treatment or is progressing. Following surgery for colon cancer, regular CEA tests detect if the cancer has returned. A rising CEA level can signal a recurrence, sometimes even before other signs appear. Pre-treatment CEA levels can also provide information about the likely course of the disease, with higher levels indicating a more advanced stage or a poorer prognosis.