Tumour markers are blood tests sometimes used in gastroenterology and hepatology.

Common ones you’ll see:

AFP (alpha-fetoprotein)
CA19-9
CEA

They can help in certain situations, but:

They are NOT screening tests
and should NOT be used to diagnose cancer alone.

Most mild elevations are benign.

This guide focuses on when to use them and how to interpret them safely.

✅ First principle (most important)

Always ask:

Will this result change management?

If not → don’t send it.

Sending tumour markers “just in case” causes:

false positives
unnecessary scans
anxious patients

🔵 AFP (Alpha-fetoprotein)

Think:
👉 Liver cancer marker

What is it used for?

Main use:

Hepatocellular carcinoma (HCC) surveillance

Especially in:

cirrhosis
chronic hepatitis B/C

Often combined with:
👉 ultrasound liver

When to request AFP

Appropriate:

Cirrhosis surveillance
Known liver mass
Suspected HCC

Not appropriate:

Mild abnormal LFTs
Fatty liver
General cancer screen

How to interpret

Mild elevation

Common in:

active hepatitis
cirrhosis
inflammation

Does NOT mean cancer

Markedly high / rising AFP

More concerning for:

Especially:

new liver lesion on imaging

Trend matters more than single value.

🔵 CA19-9

Think:
👉 Pancreatic/biliary marker

What is it used for?

Mainly:

pancreatic cancer
cholangiocarcinoma
biliary malignancy

Mostly used for:
👉 monitoring known cancer

Not diagnosis.

When to request

Appropriate:

Known pancreatic/biliary cancer follow-up
Suspicious mass already seen on imaging

Not appropriate:

Abdominal pain only
Routine workup
Screening

Important pitfall (very common exam + ward issue)

CA19-9 rises in:

cholangitis
obstructive jaundice
gallstones
pancreatitis
benign obstruction

So:

High CA19-9 + jaundice
≠ cancer automatically

Always repeat after obstruction resolves.

Very common mistake.

🔵 CEA (Carcinoembryonic antigen)

Think:
👉 Colorectal cancer marker

What is it used for?

Main use:

Monitoring known colorectal cancer after surgery

Detects:

recurrence

Not diagnosis.

When to request

Appropriate:

known colorectal cancer follow-up

Not appropriate:

unexplained anaemia
rectal bleeding
screening

These patients need colonoscopy, not CEA.

Important pitfall

CEA rises in:

smokers
inflammation
liver disease
pancreatitis

Mild elevation is common and non-specific.

Don’t overreact.

✅ Practical summary table

Marker	Think	Main use	Don’t use for
AFP	HCC	cirrhosis surveillance	screening everyone
CA19-9	pancreatic/biliary	monitoring known cancer	diagnosing obstruction
CEA	colorectal	post-op monitoring	diagnosing CRC

✅ Step-by-step ward thinking

When someone suggests a tumour marker:

Ask:

Do we already suspect a specific cancer?
Is there imaging evidence?
Will this change management?

If no → don’t send.

Imaging is usually more useful than tumour markers.

✅ Practical scenarios

Scenario 1

Cirrhotic patient for HCC surveillance
→ AFP + ultrasound appropriate

Scenario 2

Obstructive jaundice, CA19-9 high
→ treat obstruction first, repeat later
→ don’t assume cancer

Scenario 3

Iron deficiency anaemia
→ colonoscopy
→ NOT CEA

Scenario 4

Known colorectal cancer post-resection
→ CEA for recurrence monitoring

Scenario 5

Fatty liver with mildly raised AFP
→ usually benign
→ don’t panic

❌ Common junior mistakes

Using tumour markers to “rule out cancer”
Ordering them before imaging
Panicking over mild elevations
Using CEA for CRC diagnosis
Sending CA19-9 in every jaundiced patient
Forgetting benign causes

Remember:
Tumour markers are supportive, not diagnostic.

✅ Simple rule to remember

Think:

AFP → liver
CA19-9 → pancreas/bile ducts
CEA → colon

And:

👉 Use for monitoring, not screening

✅ Take-home concept

Tumour markers rarely diagnose cancer on their own.
Use them in the right clinical context, and always interpret alongside imaging.