CA 125 (Ovarian Cancer Marker)

CA 125 (cancer antigen 125) is a protein found in the blood that can be raised in certain conditions affecting the ovaries. It is best known as a tumour marker for ovarian cancer, where levels are often elevated, and it is widely used to support diagnosis and to monitor the condition.

What it can help assess

• Supporting the investigation of ovarian cancer, particularly in women with symptoms or an identified ovarian mass
• Monitoring known ovarian cancer, by tracking how levels change during and after treatment to help assess response and check for recurrence
• Assessing risk in higher-risk individuals, such as those with a strong family history

An important note on interpretation

CA 125 is not a standalone test for ovarian cancer. Levels can be raised by a number of common, non-cancerous conditions, including endometriosis, fibroids, pelvic inflammation, and even menstruation or pregnancy. Equally, some ovarian cancers do not raise CA 125 at all, particularly in the early stages. For these reasons the result is always interpreted alongside symptoms, examination, imaging such as an ultrasound scan, and other clinical information rather than on its own.

Why it matters

When used in the right context, CA 125 is a valuable tool for investigating and monitoring ovarian conditions. It is most useful as part of a wider assessment, and any raised or abnormal result should be discussed with your GP or specialist to determine the appropriate next steps.