Tumour markers CA 15-3 and CEA in metastatic breast cancer

CA 15-3 and CEA are tumour markers: substances that can be measured in a blood sample and that are sometimes made in larger amounts by breast cancer cells. In metastatic breast cancer, doctors may use them alongside scans and your symptoms to help judge whether treatment is working. A falling level over several tests often fits with the cancer responding, while a steadily rising level may suggest the cancer is growing. However, these markers have important limits. They are not raised in everyone with breast cancer, so a normal result does not mean there is no cancer. They can also rise for reasons unrelated to cancer, such as liver or lung conditions, inflammation, kidney problems, smoking or even laboratory variation. In the first weeks of a new treatment, the level can briefly go up as cancer cells break down, even when treatment is working. For these reasons, tumour markers are never used alone to diagnose breast cancer, to screen healthy people, or to change treatment without other evidence. Most guidelines do not recommend routine marker testing after treatment for early breast cancer.

How the test is done

A simple blood sample is taken, often on the same day as other blood tests before a treatment cycle. No special preparation is usually needed.

Trends matter more than single results

Doctors look at the pattern over several tests, ideally done at the same laboratory, rather than reacting to one reading.

Ask about your results

Ask whether your markers were raised at the start, because markers are most useful for people whose levels were high when the metastatic cancer was found.

A number on a blood report can feel very precise, which makes marker results easy to over-read. Understanding their limits can save a great deal of worry.

Many people never have raised markers

A significant proportion of people with metastatic breast cancer have normal CA 15-3 and CEA levels even when cancer is active. For them, scans and symptoms guide care.

Small changes are common

Results can vary slightly from test to test and between laboratories. A small rise is often not meaningful on its own.

Markers do not show where cancer is

Even when a marker rises, it cannot show which part of the body is affected, so scans are still needed.

Treatment is not changed on markers alone

Guidelines advise against stopping a treatment based only on a rising marker without other signs of progression.

What this page cannot tell you

It cannot interpret your numbers. Ask your oncologist what your trend means.

Many people find themselves checking marker results before every cycle, and each change can shape the mood of the whole family. This is a very common experience.

Keep a simple record

A list of dates and values, done at the same laboratory, makes trends easier to see and less alarming than single numbers.

Wait to discuss results

Reports often arrive by phone or online before you see your doctor. Try to discuss them together rather than interpreting them alone or searching online.

Decide what you want to know

Some people prefer not to track every number and rely on their team to flag important changes. Either approach is reasonable.

Get support

Counsellors and support groups can help with the anxiety that often comes with waiting for results, sometimes called scanxiety.

Families often see blood reports first, especially when they collect them from the laboratory or receive them on a phone. A rising number can cause alarm at home before anyone has spoken to the doctor.

Share results calmly

If you collect a report, try to share it together with the person and plan to discuss it with the oncologist, rather than reacting to a single value.

Keep the records organised

A simple folder or phone note with dates, values, laboratory names and scan results helps the team see the full picture at each visit.

Avoid unnecessary extra tests

Repeating markers at different laboratories between appointments usually adds confusion rather than clarity.