Carcinoembryonic antigen (CEA) is a glycoprotein involved in cell adhesion, normally produced in fetal gut tissue and suppressed after birth. In adults, its levels are typically low or undetectable. However, some cancers — especially gastrointestinal — can reactivate the production of CEA, making it a useful tumor marker.

Importantly, CEA is not a screening test for the general population, but rather a monitoring tool in patients with diagnosed or suspected malignancies.

Physiological and Pathological Background

CEA belongs to the immunoglobulin superfamily and is mainly secreted by tumors derived from endodermal tissues, particularly those affecting the colon, rectum, pancreas, and lungs.

CEA can also be elevated in non-malignant conditions, making clinical context critical for interpretation.

Normal Range and Interpretation

Smoking can moderately increase CEA levels due to chronic epithelial stimulation. Always consider smoking status in interpretation.

Clinical Uses of CEA in Oncology

1. Postoperative Surveillance in Colorectal Cancer

CEA is most commonly used in colorectal cancer follow-up after curative surgery. Rising levels may indicate recurrence, even before radiologic evidence appears. Guidelines often recommend monitoring CEA every 3–6 months for 3 years post-surgery.

Example: A patient with stage II colon cancer has CEA 2.5 ng/mL after surgery. One year later, it rises to 6.8 ng/mL. Imaging reveals liver metastasis not previously seen.

2. Assessment of Response to Therapy

In metastatic colorectal or pancreatic cancer, CEA can track response to chemotherapy. A declining trend may indicate tumor shrinkage; a sudden rise could suggest resistance or progression.

However, transient increases (CEA “spikes”) can occur after the first cycle of chemotherapy due to tumor lysis.

3. Prognostic Significance

High preoperative CEA levels are often associated with:

• Larger tumor burden
• Nodal involvement
• Higher risk of recurrence
• Worse overall survival

This makes it a valuable prognostic marker, particularly in colorectal and gastric cancers.

Conditions Where CEA May Be Elevated (Non-Cancer)

Thus, mild elevations (5–10 ng/mL) require caution and must be contextualized.

CEA and Specific Cancer Types

Note: CEA is not useful in hepatocellular carcinoma (AFP preferred) or prostate cancer (PSA preferred).

When Should CEA Be Measured?

CEA is not for screening. It is recommended in:

• Diagnosed colorectal cancer (pre- and post-surgery)
• Suspected recurrence (based on symptoms or imaging)
• Monitoring response in metastatic disease
• Cases of unknown primary cancer when other markers are negative

Routine measurement in healthy individuals is discouraged.

Limitations and Pitfalls

• Low specificity: Can rise in benign diseases
• Not produced by all tumors: Some cancers don’t elevate CEA at all
• Not suitable for early diagnosis: Early-stage cancers may show normal levels
• False elevations: Inflammation, infection, and smoking may cause moderate increases

Therefore, CEA should never be used alone to diagnose or rule out cancer.

Case Example

Patient A, 62 years old, non-smoker, post-op stage III colon cancer.
Initial CEA: 3.2 ng/mL → 2.4 → 2.8 → suddenly 7.5 ng/mL at 12-month visit.
CT scan reveals isolated liver lesion → confirmed recurrence.
CEA was first indicator before any symptoms or radiologic suspicion.

The Role of CEA in Modern Oncology

CEA remains a valuable, cost-effective tool in the oncologist’s arsenal, particularly for colorectal cancer. While not a stand-alone diagnostic test, it plays a key role in monitoring, early detection of recurrence, and evaluating treatment response.

When interpreted correctly and in clinical context, CEA helps clinicians make timely and targeted decisions, sometimes weeks or months before imaging catches up.

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