What does the CEA (Carcinoembryonic Antigen) test measure?

What Does CEA Test For?

Carcinoembryonic antigen (CEA) is a glycoprotein tumor marker primarily used to monitor colorectal cancer, but it is not recommended as a screening test due to its low sensitivity and specificity for early cancer detection. 1

Definition and Biology of CEA

CEA is a glycoprotein with the following characteristics:

• Molecular weight of approximately 200,000 daltons 2
• Beta-globulin electrophoretic mobility 2
• Produced by 90% of colorectal cancers 3
• Part of a family of 32 genes that are normally expressed in various tissues 4

Clinical Applications of CEA Testing

Not Recommended For:

• Screening for colorectal cancer - The American Society of Clinical Oncology (ASCO) explicitly states that CEA should not be used as a screening test for colorectal cancer due to its low sensitivity for early-stage disease 5, 1
• Initial diagnosis of cancer - CEA lacks sufficient sensitivity and specificity for primary diagnosis 1

Recommended Uses:

1. Preoperative prognostic assessment:

   • May be ordered preoperatively in colorectal cancer patients to assist with staging and surgical planning 5
   • Elevated preoperative CEA (≥5 ng/mL) correlates with poorer prognosis 5, 3

2. Postoperative surveillance:

   • For monitoring patients with stage II or III colorectal cancer every 3 months for at least 3 years 5, 1
   • Can detect recurrence before clinical symptoms appear 5
   • Most sensitive for detecting liver metastases (73.3%) 6

3. Monitoring response to treatment in metastatic disease:

   • Used in conjunction with imaging, history, and physical examination 5
   • Helps identify treatment failure when disease is not readily measurable 5

Interpretation and Limitations

Normal vs. Elevated Levels:

• Traditional cutoff for abnormal CEA is 5 ng/mL in most US laboratories 1
• CEA positivity may be defined as >2.5 ng/mL, though 5 ng/mL is considered more realistic 2
• Markedly increased values (>25 ng/mL) are highly suggestive of metastatic cancer, particularly hepatic metastasis 2

Important Limitations:

• Low sensitivity for early-stage disease (approximately 59%, range 33-83%) 1
• False positives in numerous non-cancer conditions 1, 4
• Transient elevations may occur during the first 4-6 weeks of chemotherapy 5, 1

Non-Cancer Causes of Elevated CEA:

• Inflammatory conditions: gastritis, diverticulitis, inflammatory bowel disease
• Pulmonary conditions: COPD, lung fibrosis
• Metabolic disorders: diabetes, uremia
• Liver diseases
• Advanced age (>65 years) 4
• Smoking 2

CEA in Other Cancers

While primarily used for colorectal cancer, CEA can also be elevated in:

• Pancreatic cancer 4
• Lung cancer 4
• Breast cancer (though less commonly elevated than MUC-1 assays like CA 27.29 or CA 15-3) 5
• Other gastrointestinal malignancies 2

For breast cancer specifically, ASCO does not recommend CEA for screening, diagnosis, staging, or routine surveillance after primary therapy. However, it may be used in conjunction with other markers to monitor metastatic breast cancer during active therapy 5.

Monitoring Recommendations

For colorectal cancer patients:

• Stage I: Every 6 months for 5 years 1
• Stages II-III: Every 3 months for 3 years, then every 6 months until 5 years postoperatively 5, 1
• Stage IV after complete resection: Every 3 months for 3 years, then every 6 months until 5 years 1

A rising CEA should be confirmed by retesting and warrants further evaluation for metastatic disease, but does not alone justify the institution of adjuvant or systemic therapy 5.