Tumour markers during chemotherapy: what they can and cannot show

Sometimes, for some cancers, and only as one part of the picture. Tumour markers are substances, usually proteins, found in the blood at higher levels when certain cancers are present. Examples include CEA, often used in bowel cancer, PSA in prostate cancer, AFP in liver and some testicular cancers, hCG in some testicular and pregnancy-related cancers, and markers used in ovarian and pancreatic cancers. When a cancer produces a marker, a steady fall during treatment can support other signs that treatment is working, and a sustained rise may prompt the oncologist to check with a scan. In a few cancers, such as some testicular cancers, markers are central to decisions. In many others, they are supportive rather than decisive.

Markers have important limits. Not every cancer produces a marker, and some people with a cancer type that often raises a marker never have raised levels. Levels vary naturally from test to test, and different laboratories can give slightly different results for the same sample. Markers can rise for reasons unrelated to cancer: smoking can raise CEA; liver disease, inflammation, infections and some benign conditions can raise others. Early in treatment, markers sometimes rise briefly as tumours break down, before falling, a pattern called a marker flare. For these reasons, oncologists look at trends over several tests, done in the same laboratory where possible, and always interpret markers alongside scans and examination.

Many people track their marker numbers closely, and it is understandable to want a sense of control. But small changes often mean nothing, and reacting to every rise or fall can cause great anxiety. It is best to ask your oncologist how markers are used in your case, what kind of change would matter, and to leave interpretation to them. This page explains how markers work; it cannot interpret your own results.

Trends matter more than single results

A pattern over several tests is more meaningful than one number.

Use the same laboratory

Different laboratories can report slightly different values.

Scans remain the main measure

For most solid cancers, scans guide decisions, with markers as support.

It cannot tell you what your marker results mean, whether a change is significant, or what it says about your future. Your oncologist interprets markers alongside scans and your full history.

It also cannot tell you the normal range for your laboratory. Ranges differ between laboratories and tests.

Should you track your markers?

Keeping a simple record of dates and results can help you follow conversations with your oncologist. But try not to calculate percentages or compare with online charts, and avoid ordering extra marker tests on your own. Extra tests without a clear plan often cause worry without changing care.

When a marker rises

A single rise is often not significant. Your oncologist may repeat the test, wait for the next planned scan, or arrange an earlier scan if the rise is large, sustained, or accompanied by symptoms. Ask what they plan to do and why.

When a marker falls but scans do not change

Markers and scans do not always move together. Your oncologist weighs both, and scans usually carry more weight for decisions in solid cancers.

Markers that were never raised

If your marker was normal at diagnosis, it is unlikely to be useful for tracking your treatment, and scans will be relied on instead.

Markers after treatment

Some markers are checked during follow-up after treatment. Your team will explain whether this applies to you.

Coping with marker anxiety

Waiting for marker results can cause as much worry as waiting for scans. Ask your team how and when results will be shared, and consider waiting until your appointment rather than checking results online.

Markers in testicular cancer

In testicular cancer, markers such as AFP and hCG are especially important. They are used at diagnosis, during treatment and in follow-up, and changes in these markers can guide decisions more directly than in many other cancers. Your oncologist will explain how they are used in your care.

Markers in prostate cancer

PSA is widely used to monitor prostate cancer during and after treatment. Some treatments cause PSA to fall very low, while others may cause a temporary rise before it falls. Decisions about changing treatment usually depend on patterns over time together with scans and symptoms.

Markers in ovarian cancer

In ovarian cancer, a marker is often measured before each cycle. A steady fall supports response, but levels can also be raised by inflammation in the tummy, periods or other conditions. Oncologists usually confirm any concern with scans.

Markers in bowel cancer

CEA is used in bowel cancer, particularly during follow-up after treatment. Levels can be raised in smokers and in some bowel and liver conditions, so a rise is checked carefully before conclusions are drawn.

How often markers are tested

Your oncologist decides how often markers are checked, often before each cycle or at follow-up visits. More frequent testing rarely adds useful information.

When markers and symptoms disagree

If markers look good but you have new symptoms, report the symptoms. Symptoms can matter even when markers are normal, and your team may arrange a scan.

Newer blood tests

Newer blood tests that detect cancer DNA in the blood are being studied and used in some situations. They are different from traditional markers, and your oncologist can explain whether they are relevant to you.

What to do next

Ask whether markers are used for your cancer, what change would matter, and how often they will be checked; use the same laboratory; avoid extra tests on your own; and discuss results with your oncologist.