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Ovarian cancer risks and causes

This information is about risk factors for epithelial ovarian cancer, which makes up almost 9 out of 10 cases (90%) of ovarian cancer. Epithelial means surface layer. So this is cancer of the surface layer covering the ovary.

We do not know exactly what causes epithelial ovarian cancer. But there are some things that may increase the risk. And other factors that seem to reduce it.

As with most cancers, the risk of developing ovarian cancer increases with age. Most cases are in women who are past their menopause. A family history of cancer is one of the most important risk factors for ovarian cancer. About 1 in 10 ovarian cancers (10%) are caused by an inherited faulty gene.

Other possible risk factors include infertility, using HRT, being overweight or tall and having endometriosis.
 

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How common ovarian cancer is

Around 7,100 women are diagnosed with ovarian cancer in the UK each year. This makes ovarian cancer the 5th most common cancer in women, after breast, lung, bowel 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. We have information about this and the rare types of ovarian cancer in our section on types of ovarian cancer.

 

What risk factors are

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.

 

Factors that may increase ovarian cancer risk

We don't know exactly what causes epithelial ovarian cancer. But some factors may increase the risk. Other factors seem to reduce it and are listed at the bottom of this page. 

Many factors seem to be related to how the ovaries work. When one of your ovaries produces an egg (ovulation), 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.

We have known there is a link between ovulation and ovarian cancer for a long time. But researchers are also interested in other factors that might affect ovarian cancer risk, such as hormones and inflammation. These days doctors think that there are several factors involved in the development of ovarian cancer. They call this multi factorial. 

The risk of ovarian cancer may be increased by the following factors.

 

Getting older

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.

 

Inherited faulty genes

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 3 times the risk of ovarian cancer than 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 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 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
  • 2 relatives diagnosed with ovarian cancer at any age, from the same side of the family

A close relative means a parent, brother or sister, daughter or son, grandparent, aunt or uncle, nephew or niece, half brother or half sister. 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 are worried about your family history of ovarian cancer, speak to your GP. They can tell you whether you need to be referred to your local genetics service. The genetic specialist can assess you and tell you if there are any tests you could have. And they can talk to you about ways of reducing your chance of getting ovarian cancer. 

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

 

Previous 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 around 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 more than 5 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.

 

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. A 2013 Cochrane review looked at the risk of ovarian cancer in women who took fertility drugs. The reviewers found no strong evidence that women who took fertility drugs had an increased risk of ovarian cancer. But there may be an increased risk of borderline ovarian tumours in infertile women treated with IVF. You can read this review on fertility drugs and ovarian cancer risk in the Cochrane library. It was written for researchers and specialists so it is not in plain English. 

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. A more recent study showed that using a coil for a short time lowered the risk of ovarian cancer, although the risk went up with longer use. We need more studies to confirm whether IUD's affect ovarian cancer risk.

 

Using hormone replacement therapy (HRT)

In the UK, less than 1 in 100 (1%) of ovarian cancers are linked to hormone replacement therapy (HRT) use. There are several different types of HRT, including

  • 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. 

In 2012, researchers combined all the information from 47 studies looking at ovarian cancer risk and BMI. They looked at all the results together. The researchers only saw a link between high BMI and ovarian cancer risk in women who had never used HRT. So HRT may play a part in this. 

Research has also found that taller women have a higher risk of ovarian cancer than shorter women.

 

Having endometriosis or ovarian cysts

Research has shown that women with endometriosis had a slight increase in their ovarian cancer risk. A large Swedish study has also shown that women who were admitted to hospital for ovarian cysts before the age of 29 had around double the usual risk of ovarian cancer later in life. 

 

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. 

A separate meta-analysis also found no increased risk of ovarian cancer in women using talc dusted contraceptive diaphragms. But 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 an increased risk for mucinous ovarian tumours in current smokers. But the risk went back down to normal some time after stopping smoking. 

Recent results from the EPIC study also showed that smoking increases the risk of mucinous type ovarian tumours. For other types of ovarian tumours, there was a variation in how much smoking affected risk. 

 

Diet factors

There has been a lot of research into the effect of dietary factors on ovarian cancer risk and so far most findings have been inconclusive and inconsistent. This may be because there is either no link between diet and ovarian cancer, or it is very small. Or it might be because of problems with the design of the studies.

Some studies have shown that a diet high in fats, particularly animal fats, may increase your risk of ovarian cancer. But more research is needed before we know whether changing our diet can reduce the risk of ovarian cancer. 

 

Protection factors for ovarian cancer

Your risk of ovarian cancer may be lowered by

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. For a long time we thought this is because you are not producing any eggs while you are on the pill. If your ovaries make fewer eggs during your lifetime, then the cells don't have to divide as much. So doctors think that there is a lower chance that damage will occur that could lead to cancer. Recently, researchers also think that the hormone progesterone may play a part in protecting the ovaries. Progesterone is one of the hormones in the contraceptive pill.

Research has shown that the longer you take the pill, the more your risk is thought to come down. The reduction in risk lasts for at least 30 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. 

Some research evidence seems to show 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.

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 breastfeeding frequently.  A meta-analysis published in 2013 showed that women who breastfed  had a lower risk of getting ovarian cancer compared with women who never breastfed. The risk was lower in women who breast fed for a longer time. 

Having a hysterectomy or having your tubes tied

Having your tubes tied because you don't want any more pregnancies is called sterilisation. Two recent meta-analysis studies combined the results from all of the research looking at this. These studies both found that having your tubes tied reduces the risk of ovarian cancer. Research has shown that having your womb removed (hysterectomy) may also reduce your risk of ovarian cancer. But some studies do not show any reduction in risk. 

Some types of painkillers

Some research studies seem to show that aspirin may slightly lower ovarian cancer risk and some studies seem to show that it doesn't. 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.

Remember that 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.

Taking paracetamol does not seem to affect ovarian cancer risk. 

Diet

Women with a diet high in soy, green tea and beta carotene (found in high levels in carrots, sweet potatoes and pumpkins) have a lower risk of ovarian cancer compared to women with low amounts in their diets. Non-starchy vegetables (such as broccoli, cabbage and onions) may also decrease ovarian cancer risk but the evidence is uncertain. 

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Updated: 15 January 2014