Ovarian cancer - Causes of ovarian cancer

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

Cancer begins with a change (mutation) in the structure of the DNA in cells, which can affect how they grow. This means that cells grow and reproduce uncontrollably, producing a lump of tissue called a tumour.

In ovarian cancer, cells in the ovary start to change and grow abnormally. If the cancer isn't identified at an early stage, it can spread to the abdomen and pelvis, including other parts of the female reproductive system.

Increased risk

The exact cause of epithelial ovarian cancer (the main type) isn't known, but certain things may increase your risk of developing it.

Age

Your risk of ovarian cancer increases with age, with most cases occurring after the menopause. More than 8 out of 10 cases of ovarian cancer occur in women who are over 50 years of age.

Family history

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

If your relatives developed cancer before the age of 50, it's more likely it was the result of an inherited faulty gene. BRCA1 and BRCA2 are faulty genes that are linked to ovarian cancer. They're also known to increase the risk of breast cancer.

Having relatives with ovarian cancer doesn't mean you definitely have a faulty gene in the family – the cancer could have happened by chance. Only 1 in 10 (10%) of ovarian cancers are thought to be caused by a faulty gene.

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

• one relative diagnosed with ovarian cancer at any age and at least two close relatives with breast cancer whose average age is under 60; all of these relatives should be on the same side of your family (either your mother's OR father's side)
• one relative diagnosed with ovarian cancer at any age and at least one close relative diagnosed with breast cancer under the age of 50; both of these relatives should come from the same side of your family
• two relatives from the same side of the family diagnosed with ovarian cancer at any age 

If you're at a higher risk of having a faulty gene, your GP can refer you for tests to check for faulty BRCA1 and BRCA2 genes.

Ovulation and fertility

Every time an egg is released into the reproductive system, the surface of the ovary breaks to let it out. The surface of the ovary is damaged during this process and needs to be repaired. Each time this happens, there's 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. At these times, eggs aren't released.

There's no strong evidence to show that women who have infertility treatment have an increased risk of developing ovarian cancer. However, it's thought that infertility itself may increase ovarian cancer risk and research into this area is being carried out. 

Hormone replacement therapy (HRT)

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

Endometriosis

Endometriosis may also increase your risk of ovarian cancer. In endometriosis, the 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 occurs during menstruation occurs in other parts of the body. There's no way for this endometrial tissue to leave the body so it becomes trapped, leading to pain, swelling and bleeding in that area.

More information 

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