Causes of ovarian cancer

Several possible causes of ovarian cancer have been identified, along with risks that may make developing the condition more likely.

Our bodies are made up of billions of tiny cells. Normally, cells grow and multiply in an orderly way. New cells are only made when and where they’re needed. In cancer, this orderly process goes wrong and cells begin to grow and multiply out of control.

In ovarian cancer, cells in the ovary start to change and grow abnormally. If the cancer is not identified at an early stage, it can spread to nearby parts of the body, including other parts of the female reproductive system.

Increased risk

Some of these risk factors cannot be changed, but there may be some that can. Although these factors may increase the risk of ovarian cancer, you can still contract the condition even if none of them apply to you.

Family history

If you have two or more close relatives (mother, sister or daughter) who developed ovarian cancer or breast cancer, you may be at higher risk of developing the condition.

If your relatives developed cancer before the age of 50, it may be the result of an inherited faulty gene. Faulty genes linked to ovarian cancer include BRCA1 and BRCA2. They are also known to be linked to the development of breast cancer.

Having relatives with ovarian cancer does not mean you definitely have a faulty gene in the family – the cancer could have happened by chance. About one in 10 ovarian cancers are thought to be caused by a faulty gene.

You may be at high risk of having a faulty gene if you have:

• One close relative (such as your mother, sister or daughter) diagnosed with ovarian cancer at any age, and at least two close relatives who have breast cancer. Your relatives with breast cancer should be on the same side of your family and have an average age of less than 50 years.
• One close relative diagnosed with ovarian cancer at any age, and at least one close relative with breast cancer diagnosed under the age of 40. These relatives should come from the same side of your family.

If you are concerned you may be at higher risk of ovarian cancer because of your family history, talk to your GP. If you are at high risk, your GP can refer you to a genetic counselling clinic. It is possible to test for the BRCA1 and BRCA2 genes.

Age

Your risk of ovarian cancer increases with age and most cases of ovarian cancer occur after the menopause. More than eight out of 10 cases of ovarian cancer are in women over the age of 50.

Fertility and egg release

Every time an egg is released into the reproductive system, the surface of the ovary has to break to let it out. As the surface of your ovary is damaged during this process, it needs to be repaired. Every time this happens, there is a greater chance of abnormal cell growth during the repair.

This may be why the risk of ovarian cancer decreases if you take the contraceptive pill, or have multiple pregnancies or periods of breastfeeding, as during this time eggs will not be released. In contrast, some research has shown there is an increased risk of ovarian cancer in women who have infertility treatment (as more eggs may be released because of the treatment). But other studies have found this is not the case.

Hormone replacement therapy (HRT)

Women who take hormone replacement therapy (HRT) have been shown to have a small increased risk of ovarian cancer. However, if HRT is stopped, after five years the risk is reduced to the same level as women who have never taken HRT.

Endometriosis

Endometriosis may increase your risk of ovarian cancer. Endometriosis is a condition where cells that usually line the womb grow elsewhere in the body. These endometrial cells behave as if they were in the womb, so thickening and bleeding that usually happens during menstruation occurs in this other part of the body. But there is no way for this endometrial tissue to leave the body and it becomes trapped, leading to pain, swelling and bleeding in that area.

Want to know more?

• Target Ovarian Cancer: Risk factors for ovarian cancer 
• Target Ovarian Cancer: When ovarian cancer runs in families 
• Cancer Research UK: Ovarian cancer risks and causes