Ovarian cancer risks and causes

Almost 7,000 women in the UK are diagnosed with ovarian cancer each year.  Not including non melanoma skin cancer, this makes ovarian cancer the 5th most common cancer in women, after breast, bowel, lung and womb cancer.

Please note - this information is about risk factors for epithelial ovarian cancer, which makes up almost 9 out of 10 cases of ovarian cancer. Epithelial cancers start in the surface layer of the ovary. We have information about rare types of ovarian cancer in our section on types of ovarian cancer.

A risk factor is anything that can increase your chance of developing cancer. Different cancers have different risk factors. Some factors can lower your risk of cancer and are known as protection factors.

We don't know exactly what causes epithelial ovarian cancer. But some factors may increase the risk. Other factors seem to reduce it. Many factors seem to be related to how the ovaries work. When one of your ovaries produces an egg, the surface layer of the ovary bursts to release the egg. The surface cells then divide to repair the damage. The more eggs your ovaries produce during your life time, the more cells need to divide and the higher the chance that damage will occur that could lead to cancer. There is more about this in our section about how cancers start.

As with most cancers, the risk of developing ovarian cancer increases as you get older. Most cases are in women who have had their menopause.

Apart from getting older, your risk of ovarian cancer may be increased by

• A family history of cancer
• Having breast cancer
• Being infertile or having fertility treatment
• Using a coil (intra uterine device - IUD)
• Using hormone replacement therapy (HRT)
• Being overweight or tall
• Having endometriosis
• Using talcum powder
• Smoking
• Diet factors

A family history of cancer

Most ovarian cancers are due to gene changes that develop during a woman’s life and are not inherited. But about 1 in 10 ovarian cancers (10%) are caused by an inherited faulty gene. Faulty inherited genes that increase the risk of ovarian cancer include BRCA1 and BRCA2. These genes also increase the risk of breast cancer.

If you have very close relatives who have had ovarian cancer or breast cancer you may be more at risk of developing ovarian cancer than other women in the population. A very close relative means a mother, sister or daughter. If your relatives were under 50 years old when their cancers were diagnosed, it is more likely that their cancer is due to an inherited faulty gene.

Having relatives with ovarian cancer does not necessarily mean that you have a faulty inherited gene in the family. The cancers could have happened by chance. But women with a mother or sister diagnosed with ovarian cancer have two to three times the risk of ovarian cancer of women without a family history.

Tests can now check for faulty BRCA1 or BRCA2 genes. Your GP can refer you to your local genetics service to assess whether you could be at risk of having a faulty gene if you have

• 1 close relative diagnosed with ovarian cancer at any age and at least 2 close relatives with breast cancer with an average age of under 60 - all from the same side of your family (either your mother's OR father's side)
• 1 close relative diagnosed with ovarian cancer at any age and at least 1 close relative diagnosed with breast cancer before 50 years old, both from the same side of the family
• 1 close relative diagnosed with breast cancer before they were 50 years old and ovarian cancer at any age

A close relative means a parent, brother or sister, grandparent, aunt or uncle, nephew or niece. To get the average age of 2 relatives, add the ages together and divide by 2. So if one relative was 35 and the other 65, the average age is 50.

Doctors have identified some situations that make it very likely there is an inherited faulty gene in a family. These are called family syndromes. They are families with several close relatives who have

• Breast or ovarian cancer
• Only ovarian cancer
• A variety of cancers including ovary, bowel, prostate, lung, stomach, womb lining (endometrium) or lymphoma

If you have two close relatives with ovarian cancer, you may be able to be tested regularly (screened) to check for ovarian cancer. You can ask your GP to get you an appointment with your local genetics service for assessment.

If you would like to check your own breast or ovarian cancer risk you can use the OPERA online interactive tool.

Having breast cancer

Breast cancer and ovarian cancer can sometimes be due to the same faulty genes. Women who have had breast cancer have up to double the risk of developing ovarian cancer compared to other women in the population, and if their breast cancer was diagnosed before the age of 40, their risk is almost four times higher.

Some factors are indicators that breast cancer could be due to a faulty gene - and the same gene fault could cause ovarian cancer. These factors are listed below.

• If you had breast cancer before 40 years old, and have a family history of breast cancer, you have 6 times the risk of the average woman.
• If you had breast cancer before 40 and have a family history of ovarian cancer, you have 17 times the average risk of ovarian cancer.

If you think you may have a faulty gene, you can speak to your GP. There is more information about screening for ovarian cancer in this section of CancerHelp UK.

Being infertile or having fertility treatment

Some older studies showed a link between taking fertility drugs and an increased risk of ovarian cancer. But more recent research doesn't support this. It is more likely that infertility itself increases ovarian cancer risk, rather than fertility treatment being the cause. More research is going on to try to clarify this. 

Using a coil (intra uterine device - IUD)

One research study has shown that women who use a coil (IUD) for birth control have an increased risk of ovarian cancer, but the risk is still small. We need more studies to confirm that IUD's increase ovarian cancer risk.

Using hormone replacement therapy (HRT)

There are several different types of hormone replacement therapy

• Oestrogen only HRT
• Continuous combined HRT - oestrogen and progesterone
• Combined sequential HRT - continuous oestrogen with progesterone as well for 15 days of the cycle

These types of HRT have slightly different levels of cancer risk. So if you are looking at research about HRT, it is helpful to make sure you know which type the research is about. In ovarian cancer, most studies show that oestrogen only HRT increases ovarian cancer risk, including the Million women study published in 2007 and a combined analysis of studies published in 2009.

Most women who take HRT these days, take one of the types of combined HRT. Some studies (including the Million women study) have shown that these can also increase the risk of ovarian cancer if they are taken for longer than 5 years. The longer women take HRT, the more the risk increases. When women stop taking HRT the risk goes back down over a few years to the same level as women who have never taken HRT.

Being overweight or tall

You can see if you are obese or overweight for your height by working out your body mass index. In 2008 researchers analysed 12 studies which looked at the risk of being overweight in premenopausal and postmenopausal women. The analysis found that the risk of ovarian cancer was higher in premenopausal women with a BMI over 30, but there was no effect in postmenopausal women. However, since this analysis, three large studies (including the EPIC study) have shown that postmenopausal women who are obese have a higher risk of ovarian cancer. Research has also found that taller women have a higher risk of ovarian cancer than shorter women.

Having endometriosis or ovarian cysts

A large Swedish study that combined hospital records with data from cancer registries found that women with endometriosis had a slight increase in their ovarian cancer risk. This study also showed that women who were admitted to hospital for ovarian cysts before the age of 29 had double the usual risk of ovarian cancer later in life. A study in 2004 showed that women who had removal of an ovary or other surgery to treat ovarian cysts had an almost nine times increased risk of ovarian cancer.

Using talcum powder

Using talcum powder between your legs has been thought to increase the risk of ovarian cancer. The powder could, in theory, travel up into the vagina and then through the cervix into the womb. If it then worked its way down the fallopian tubes to the ovaries, it could get into the ovaries themselves and cause irritation. Constant irritation could potentially cause inflammation and lead to cancerous changes in cells.

In 2003, researchers carried out a meta-analysis of 16 studies of talc and ovarian cancer risk. This means they combined all the information from the studies and looked at the results together. The combined results showed that there could be a small increased risk of developing ovarian cancer if you use talc. But the researchers decided that this was probably a statistical blip, because the risk of ovarian cancer didn't increase more if women used larger amounts of talc.

A separate meta-analysis also found no increased risk of ovarian cancer in women using talc dusted contraceptive diaphragms. But three further studies have shown an increased risk of ovarian cancer in women regularly using talc, and the risk increased with heavier use of talc. So the evidence on this issue is inconsistent and research is continuing. One study has looked at whether talc may increase the risk of certain types of ovarian cancer in women with particular genes.

Smoking

An analysis combining the results of several individual studies showed a doubling of ovarian cancer risk for mucinous ovarian tumours in current smokers. But the risk went back down to normal some time after stopping smoking. There was no change in the risk for serous or endometrioid cancers but current smokers had a reduced risk of clear cell ovarian tumours.

Diet factors

A review of 12 studies seemed to show that a diet very high in saturated fat increases the risk of ovarian cancer. Another review of several studies showed that a very high intake of lactose (found in milk) increased ovarian cancer risk.

Your risk of ovarian cancer may be lowered by

• Taking the contraceptive pill
• Having children
• Breast feeding
• Having a hysterectomy or having your tubes tied
• Some types of painkillers
• Plant oestrogens

Taking the contraceptive pill

Taking the contraceptive pill at some point in your life reduces your risk of cancer of the ovary quite a bit. This is because you are not producing any eggs while you are on the pill. The longer you take the pill, the more your risk is thought to come down. The reduction in risk lasts for at least 20 years after you stop taking the pill.

Having children

Having children seems to reduce ovarian cancer risk. The risk decreases the more children a woman has. A woman who has had three or more children has half the risk of women who have had no children.

Some research evidence seems to show that that having your last child after 35 reduces the risk of ovarian cancer, compared to women who have their last pregnancy before they are 25, however many children you have. There is also evidence that miscarriage or abortion protect against ovarian cancer. Having children is protective for the same reason as taking the pill - while you are pregnant, your ovaries don't produce any eggs.

These increases and decreases in risk have been picked up in very large surveys of women's health. This type of risk factor is assessed by looking at statistics on large populations overall. It isn't likely to make much of a difference to any individual woman.

Breast feeding

Having breastfed your children may lower the risk of ovarian cancer and of some types in particular. This may be because your ovaries normally stop producing eggs each month while you are breast feeding frequently. But one large study showed no effect of breast feeding on ovarian cancer. A Cancer Research UK study published in 2011 found that breast feeding for more than 6 months can reduce your risk of developing ovarian cancer. 

Having a hysterectomy or having your tubes tied

Having your tubes tied because you don't want any more pregnancies is called sterilisation. Some studies show that it reduces the risk of ovarian cancer but other studies don't show any reduction in risk so the situation is not really clear. Having your womb removed (hysterectomy) may also reduce the risk.

Some types of painkillers

Some research studies seem to show that aspirin may lower ovarian cancer risk and some studies seem to show that it doesn't. A large study published in January 2006 found that anti inflammatory painkillers, including aspirin, can lower the risk of ovarian cancer. They also found that paracetamol lowered risk, but not quite as much as aspirin. We need further research to find out more about this, because a study that combined all the research results showed no link between aspirin or anti inflammatory painkillers and the risk of ovarian cancer. A recent large American study also found no link with any type of painkiller , while 2 other studies actually found that anti-inflammatory drugs increase risk of ovarian cancer. A separate meta-analysis that combined all the studies looking into paracetamol and ovarian cancer risk showed that regular use of paracetamol reduced risk by about a third.

Remember - aspirin can be dangerous and you should talk to your own GP before starting to take it regularly. It can irritate the lining of your stomach and cause bleeding. You certainly shouldn't take it if you have any history of stomach ulcer.

Plant oestrogens

Plant oestrogens known as phyto oestrogens are found in soy foods, pulses (beans, lentils and peas), a range of plant foods, and tea, coffee and cereals. Some studies have shown that phyto oestrogens can reduce ovarian cancer risk.