Tumor markers in digestive cancers: a complete guide for patients (CEA, CA 19-9, CA 72-4 and AFP)

Have you done tests and seen values such as “CEA”, “CA 19-9” or “AFP” increased? Before you panic, it is essential to know a basic principle valid in 2026: these markers are not used for screening in healthy people and, taken individually, cannot diagnose cancer. Their true value appears in monitoring treatment and tracking the evolution of the disease. This guide explains, in a way that everyone can understand, what each digestive marker means and how it guides medical decisions.

1. CEA (Carcinoembryonic Antigen): the “barometer” of colorectal cancer

CEA is the best-known marker in digestive cancers. It is a glycoprotein produced normally in fetal life, but which reappears in many tumors. The reference values are:

• Non-smokers: ≤3 ng/mL
• Smokers: ≤5 ng/mL

Why does smoking matter? Because smoking is the most common cause of an isolated CEA elevation , without cancer. Other benign causes include cirrhosis, inflammatory bowel disease, pancreatitis, and rectal polyps.

Here is how the values are interpreted:

CEA value	Possible meaning
>5 ng/mL	Possible colon/stomach/pancreatic cancer (in clinical context)
>20 ng/mL	Advanced disease, probable metastases
>100 ng/mL	Typically metastatic disease, often hepatic

The most important use of CEA is monitoring: after successful colorectal cancer surgery, CEA usually returns to normal within 4–6 weeks. A new increase after normalization may signal a recurrence 3–6 months before imaging . Therefore, ASCO recommends monitoring CEA every 2–3 months for a minimum of 2 years in patients who have undergone surgery for stage II–III colorectal cancer.

An important prognostic detail: a study of 131,181 patients with stage I–III colon cancer showed that an elevated preoperative CEA correlates with an increased risk of mortality (HR 1.62).

2. CA 19-9: the pancreatic cancer marker (with one surprising exception)

CA 19-9 is the main marker for pancreatic cancer , being elevated in approximately 80% of patients with advanced disease. The normal value is below 37 U/mL.

Interpretation of values:

• 37–100 U/mL: often cholecystopancreatitis or benign biliary obstruction
• >100 U/mL: suggestive of pancreatic cancer
• >1,000 U/mL: metastatic disease

Here comes a fascinating detail that few patients know about: approximately 5–10% of the population has the “Lewis-null” blood type and cannot synthesize CA 19-9 at all — no matter how large the tumor, the test will always come back negative. This is why no marker is interpreted in isolation.

In 2026 practice, a CA 19-9 above 500 U/mL at diagnosis predicts poorer resectability, directing the physician to chemotherapy (FOLFIRINOX). Normalization of CA 19-9 after surgery predicts better survival.

3. CA 72-4: the “specialized” marker for gastric cancer

Less well known, but very useful, CA 72-4 is the preferred marker for monitoring gastric (stomach) cancer , being more specific than CEA alone. The normal value is below 6.9 U/mL.

• 6.9–15 U/mL: gastric ulcer, inflammatory conditions
• >15 U/mL: advanced gastric cancer or mucinous ovarian cancer

In practice, CA 72-4 is used together with CEA and CA 19-9 for more accurate monitoring of stomach cancer.

4. AFP (Alpha-fetoprotein): liver cancer marker

AFP is the main marker for liver cancer (hepatocarcinoma, HCC) , with a normal value ≤10 ng/mL. Interpretation depends strongly on the level:

• 10–200 ng/mL: chronic hepatitis, cirrhosis
• >200 ng/mL: suspected liver cancer
• >1,000 ng/mL: highly specific for HCC or germ cell tumors

A key point: over 10% of patients with liver cancer do NOT have elevated AFP . Furthermore, AFP alone has a low sensitivity for early liver cancer—only 11% at the 20 ng/mL threshold.

Therefore, in 2026, the GALAD score is used , which combines five variables (sex, age, AFP-L3%, AFP and DCP) and achieves a sensitivity of 60–80% for early detection of HCC — much higher than AFP used alone. The EASL guidelines 2024–2026 confirm biannual ultrasound ± AFP as the standard of surveillance in patients with cirrhosis.

5. Remember: three golden rules

1. Markers are not used for screening in healthy, asymptomatic individuals.
2. The trend over time (whether the value increases or decreases with repeated measurements) is much more important than a single isolated value.
3. Clinical context (imaging, biopsy) is mandatory — no marker alone makes the diagnosis.

Marker	📊 Normal value	🎯 Associated cancer	🔎 Growth meaning
THE	≤3 ng/mL (non-smokers) / ≤5 ng/mL (smokers)	Colorectal, gastric, pancreatic	>5 = colon/pancreas/stomach; >20 = advanced disease, metastases
CA 19-9	<37 U/mL	Pancreatic, biliary	37–100 = cholecystopancreatitis; >100 = pancreatic cancer; >1,000 = metastatic disease
CA 72-4	<6.9 U/mL	Gastric (stomach), ovarian mucinous	6.9–15 = gastric ulcer/inflammation; >15 = advanced gastric cancer
AFP	≤10 ng/mL	Hepatic (HCC), germ cell tumors	10–200 = hepatitis/cirrhosis; >200 = suspected HCC; >1,000 = HCC/germ cell tumor

⚠ Note (Lewis-null group): 5–10% of the population cannot synthesize CA 19-9 at all, regardless of how large the tumor is

Likewise, over 10% of patients with liver cancer do NOT have elevated AFP.

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How Artificial Intelligence helps you correctly interpret digestive markers

As you have seen, each digestive marker has its own thresholds, exceptions (such as the Lewis-null group) and correlations with specific treatments (FOLFIRINOX, FLOT, atezolizumab), and international protocols are updated from one month to the next.

Oncoexpertai platform comes in . Unlike a simple reading of the analyses, our advanced Artificial Intelligence algorithms instantly correlate your complete marker profile (CEA, CA 19-9, CA 72-4, AFP) with thousands of clinical studies and international oncology guidelines updated in real time (NCCN / ESMO). The technology does not replace the doctor, but gives him the certainty that the proposed treatment regimen is the most suitable for your specific profile.

If you just want a completely free opinion without uploading any medical documents, use one of the 2 orange boxes “Talk to Dr. Onisim” or green “Message to Dr. Onisim”

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Disclaimer: The information in this article is for informational and educational purposes only. It is not a substitute for the consultation, diagnosis, or treatment provided by a qualified medical professional. For any decision regarding your health, always consult a medical professional.

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Dr. Onisim Florin Senior Medical Oncologist | Founder of OncoExpertAI

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