Overview
Carcinoembryonic Antigen (CEA) is a non-specific serum biomarker and an oncofetal glycoprotein expressed by mucosal cells. Under normal conditions, CEA levels are low, but they may become elevated in various malignancies. CEA is most commonly associated with colorectal cancer and is also elevated in cancers such as medullary thyroid cancer, breast cancer, mucinous ovarian cancer, gastric cancer, pancreatic cancer, lung cancer, and several other malignancies. In addition to malignant conditions, CEA levels may be increased in tobacco smokers.
CEA is primarily used as a tumor marker for monitoring disease progression, treatment response, and recurrence, particularly in colorectal cancer. For detecting colorectal cancer recurrence, CEA demonstrates variable sensitivity and specificity depending on the cutoff value used. However, it is important to note that CEA is not a cancer-specific marker and may be elevated in several benign conditions. Therefore, CEA testing is mainly of prognostic and monitoring value rather than diagnostic value.
Symptoms
It itself does not cause symptoms, as it is a laboratory biomarker rather than a disease. Testing is performed in patients who present with symptoms related to malignancies or during follow-up after cancer treatment. Symptoms prompting evaluation may relate to colorectal cancer or other associated cancers and vary depending on the organ involved.
Patients undergoing CEA testing may have gastrointestinal symptoms, unexplained weight loss, fatigue, or symptoms related to metastatic disease. CEA testing is also used in asymptomatic patients during post-treatment surveillance to detect early recurrence or metastasis before clinical symptoms appear.
Causes
Elevated CEA levels are caused by increased expression or release of the antigen from malignant cells. The most common cause is colorectal cancer, particularly in advanced or metastatic disease. Other malignancies associated with elevated CEA include cancers of the small intestine, stomach, pancreas, liver, lung, breast, cervix, ovary, thyroid (medullary carcinoma), melanoma, lymphoma, osteosarcoma, retinoblastoma, choriocarcinoma, and urothelial carcinoma.
CEA elevation is not limited to malignant conditions. Several non-malignant causes are also documented, including cigarette smoking, infections, peptic ulcer disease, inflammatory bowel disease, hepatitis, liver cirrhosis, benign breast lesions, and hypothyroidism. Because of this overlap, CEA values must always be interpreted in the context of clinical findings and other diagnostic investigations.
Risk Factors
Risk factors associated with elevated CEA levels include the presence of colorectal cancer or other malignancies, especially in advanced stages or with metastatic spread, particularly to the liver. Tobacco smoking is a well-recognized risk factor and results in higher baseline CEA levels compared to non-smokers.
Chronic inflammatory conditions, liver disease, gastrointestinal disorders, and benign tumors can also increase CEA levels. Patients with a history of colorectal cancer are at higher risk of recurrence, making serial CEA monitoring valuable in follow-up care. Improper interpretation without clinical correlation may lead to false-positive or false-negative conclusions.
Prevention
There is no direct method to prevent elevated CEA levels, as CEA is a marker rather than a causative factor. However, appropriate clinical use of the test helps prevent misdiagnosis and unnecessary interventions. Baseline CEA levels should be measured at the time of initial histopathological diagnosis in colorectal cancer, allowing meaningful comparison during follow-up.
Regular monitoring of CEA levels after treatment aids in early detection of recurrence, assessment of treatment efficacy, and identification of possible metastasis. Smoking cessation may help reduce non-malignant elevation of CEA. Since CEA is neither cancer-specific nor suitable for screening, results should always be correlated with clinical examination, imaging studies, histopathology, and other tumor markers. Tissue diagnosis remains mandatory before initiating any cancer treatment, and CEA should be used primarily as a prognostic and surveillance tool rather than a standalone diagnostic test.
