CA 15-3: what it is, what it tells you and when it’s tested

CA 15-3 is a protein found in small amounts in your blood. Some breast cancers, especially when they have spread, make more of it. But it also rises for benign reasons, such as some liver conditions. It is not used to find breast cancer: it is mainly used to follow treatment of a disease that is already known.

When it’s tested

It is usually ordered by an oncologist for women with breast cancer that has spread, together with CEA and scans, to see whether treatment is working.

It is not used for screening or diagnosis. In small cancers it is often normal, and it also rises for other reasons. Breast screening uses mammography, offered by your region.

That is why Rosa does not test it. The Rosa panel is a general prevention check-up, not a cancer test: it looks at your heart, metabolism, liver, kidneys, thyroid and blood.

What it tells you, and what it does not

A high CA 15-3 does not mean cancer. Benign breast conditions, liver conditions, urinary infections, autoimmune conditions and pregnancy can raise it.

A normal CA 15-3 does not rule out breast cancer.

At the start of a new treatment, the value sometimes rises for a few weeks even when the treatment is working. That is why your oncologist always reads it together with scans.

Your doctor reads it together with other tests:

• CEA: For breast cancer that has spread, it is often measured alongside
• ALT and AST: Liver conditions can raise CA 15-3
• Urine test: A urinary infection can raise it

Normal CA 15-3 levels

The lab decides what is normal. Many lab reports give a CA 15-3 below 30 U/mL, but the limit changes with the method: your report may print a different one.

The same blood can give slightly different numbers at two labs. To follow it over time, it is best to use the same lab every time.

Why CA 15-3 can be high

There are several causes, and often they are not cancer.

• Benign breast conditions: Some benign breast conditions can raise it.
• Liver conditions: Hepatitis, chronic hepatitis and cirrhosis can raise it.
• Urinary infections: A urinary tract infection can raise it.
• Autoimmune conditions: Some autoimmune conditions can raise it.
• Pregnancy: It can be higher in pregnancy.
• Some cancers: Mainly breast cancer that has spread, but also ovarian, pancreatic, lung and bowel cancer.

If you have had breast cancer

After treatment for early breast cancer, if you feel well, check-ups are regular visits and mammograms. Italian and international guidelines advise against routine CA 15-3 and CEA: in women who feel well they have shown no benefit.

If the disease has spread, your oncologist may use them, together with scans, to follow treatment.

If you have a new symptom that does not go away, talk to your oncologist without waiting for your next check-up.

If your CA 15-3 is above the limit

Try not to worry: a high value often has other causes. Where to start:

• Show the report to the doctor who ordered it, or to your GP.
• Tell them whether you have a liver condition, a urinary infection or an autoimmune condition, or whether you are pregnant.
• Your doctor often has it repeated, at the same lab.
• Only your doctor decides whether more tests are needed. A high result on its own is not enough for a diagnosis.

When to talk to a doctor

Talk to your doctor if:

• Your CA 15-3 is above the limit on your report.
• You notice a lump in your breast or armpit, a nipple that turns inwards or blood coming from a nipple.
• You have had breast cancer and have a new symptom that does not go away, such as bone pain or a lasting cough.
• You are being treated for breast cancer and your CA 15-3 rises from one check-up to the next.

Frequently asked questions

High CA 15-3: what are the benign causes? Benign breast conditions, liver conditions, urinary infections, autoimmune conditions and pregnancy. That is why a high value, on its own, does not mean cancer.

What are normal CA 15-3 levels? Many lab reports give a value below 30 U/mL, but the limit changes with the lab’s method. The range on your own report is what counts.

Can CA 15-3 find breast cancer? No. In small cancers it is often normal, and it rises for other reasons too. Breast screening uses mammography, and a lump is checked with an examination and scans.

Do I need CA 15-3 after breast cancer? If your treatment is over and you feel well, usually not: guidelines advise visits and mammograms, not markers. Your oncologist decides, based on your history.

Does Rosa test CA 15-3? No. Rosa is a general prevention check-up and does not include tumour markers. If your doctor thinks CA 15-3 is useful, they order it separately.

Sources

• AGENAS (Italian National Agency for Regional Health Services), circulating tumour markers in oncology: a guide to appropriate clinical use, summarising guidelines including AIOM, ESMO and ASCO. Quaderno di Monitor, 2016. AGENAS 2016
• Harris and colleagues, American Society of Clinical Oncology 2007 update of recommendations for the use of tumor markers in breast cancer. Journal of Clinical Oncology, 2007. PMID 17954709
• Khatcheressian and colleagues, breast cancer follow-up and management after primary treatment: American Society of Clinical Oncology clinical practice guideline update. Journal of Clinical Oncology, 2013. PMID 23129741
• Sturgeon and colleagues, National Academy of Clinical Biochemistry guidelines for use of tumor markers in testicular, prostate, colorectal, breast, and ovarian cancers. Clinical Chemistry, 2008. PMID 19042984