Cervical cancer risks and causes
This page is about the risk factors and causes of cervical cancer. You can find the following information
- A quick guide to what's on this page
- How common cervical cancer is
- What a risk factor is
- HPV infection
- Other sexually transmitted infections
- A weakened immune system
- The pill
Human papilloma virus (HPV) is the major cause of cervical cancer. There are many different types of HPV. Some types of HPV cause genital warts and are sometimes called the genital wart virus. The types of HPV that cause warts do not usually cause cell changes that develop into cancer. Some other types of HPV are considered high risk for cancer of the cervix. HPV is passed on from one person to another through sexual contact.
Women who get cervical cancer have had past infections with HPV. High risk types of HPV can cause changes in the cells covering the cervix that make them more likely to become cancerous in time. But most women infected with these viruses do NOT develop cervical cancer. So other factors must also be needed.
Women who smoke are more likely to get cervical cancer than those who don't. Taking the pill could increase a woman’s risk of cervical cancer. It is not clear why this is. Women with a weakened immune system are also more likely to get cervical cancer and so are those who have had a large number of children.
You can view and print the quick guides for all the pages in the about cervical cancer section.
Around 3,100 women are diagnosed with cervical cancer in the UK each year. Overall, about 2 out of every 100 cancers diagnosed in women (2%) are cervical cancers. But it is the most common cancer in women under 35 years old.
Around 4 million women are invited for cervical screening each year in England. About 1 out of every 100 women screened has a moderate or high grade abnormality (1%). Early treatment can prevent these cervical changes developing into cancer.
Anything that increases your risk of getting a disease is called a risk factor. Different cancers have different risk factors. This page discusses the risk factors for cervical cancer. Even if you have one or more of the risk factors below, it does not mean that you will definitely get cervical cancer.
Human papilloma virus (HPV) is the major cause of the main types of cervical cancer – squamous cell cancer and adenocarcinoma. There are over 100 different types of human papilloma virus (HPV). At least 40 types are passed on through sexual contact. Some types are called the wart virus or genital wart virus because they cause genital warts. The types of HPV that cause warts do not usually cause cell changes that develop into cancer.
About 15 types of HPV are considered high risk for cancer of the cervix - they include types 16 and 18. These 2 types cause about 7 out of 10 cancers of the cervix (70%). If you have persistent infections with high risk types of HPV, you are more at risk of developing pre cancerous cervical cells or cervical cancer.
HPV is common. Most sexually active women will come into contact with at least one type of HPV during their lifetime. But for most the virus causes no harm and goes away on its own. So other factors must be needed for cancer to develop.
If men use a condom during penetrative sex, this reduces the risk of a woman becoming infected with HPV. Using condoms also reduces the chance of a woman developing pre cancerous changes in the cervix (CIN) if she has HPV infection.
There are now vaccines to prevent HPV infection. All girls aged 12 or 13 in the UK are routinely offered the HPV vaccine at school. These vaccines protect against the strains of HPV that are most likely to cause cervical cancer. But they don't protect against all strains. It takes 15 to 20 years for cervical cancer to develop in women with normal immune systems. But it can develop more quickly (perhaps in only 5 to 10 years) in women with weakened immune systems. So it is still important for women to carry on with cervical cancer screening. It will take some years before the introduction of the vaccine has a major effect on reducing the number of cases of cervical cancer.
A recent study looked at all the research results together and found that having both herpes and HPV infection doubled the risk of squamous cell cervical cancer. This research took account of the number of sex partners women had, as well as their use of the pill.
Another study looked at infection with HPV and chlamydia (pronounced klah-mid-ee-ah). The study found that the risk of squamous cell cancer increased by about 80% in women with both infections.
If you smoke, you are more likely to develop squamous cell cervical cancer. Researchers have found cancer causing chemicals (benzyrene) from cigarette smoke in the cervical mucus of women who smoke. They think that these chemicals damage the cervix. There are cells in the lining of the cervix called Langerhans cells that specifically help fight against disease. These cells do not work so well in smokers.
If you have a high risk type of HPV infection and smoke, you are twice as likely to have pre cancerous cells in your cervical screening test, or to get cervical cancer. The Langerhans cells are less able to fight off the virus and protect the cervical cells from the genetic changes that can lead to cancer.
A type of study called a meta analysis combines the results of several individual studies looking into a particular topic. This is more reliable than the results of a single study. A recent meta analysis showed the risk of squamous cell cervical cancer is increased by 50% in women who currently smoke. Another study has estimated that around 200 cases of cervical cancer in 2010 were linked to smoking.
Remember that if you smoke you are more likely to get cervical cancer. If you have mild pre cancerous changes in your cervical screening test, the cells are more likely to go back to normal without any treatment if you stop smoking.
If you have a weakened immune system, then your risk of many cancers, including cervical cancer, is higher than average. People with HIV and AIDS, or people taking drugs to suppress their immune systems after an organ transplant, are more at risk of developing cervical cancer if they also have HPV infection.
This is because a healthy immune system normally protects you from cells that have become abnormal. Your immune system will kill off the cells and so prevent them from becoming cancerous.
Research that looked at a number of studies together shows that taking the pill could increase a woman's risk of developing cervical cancer. It is not clear why this is. The researchers took account of other factors, such as the number of sexual partners, smoking, and most importantly, infection with HPV. Researchers suspected that there was a link with taking the pill, but clear evidence has not come out of the studies until more recently.
Before now we thought that the pill was statistically linked to cervical cancer because women on the pill are more likely to be sexually active and so more at risk of picking up HPV. Also, they do not necessarily use barrier contraception (condom or cap) which could prevent them picking up the HPV. But now it seems that it may actually directly increase the risk.
About 8 in 100,000 women get cervical cancer every year in the UK. The recent research suggests that amongst women who have taken the pill for at least 5 years, that risk is doubled. But this is still a small risk, and it is important to know that taking the pill can help to protect you against womb and ovarian cancers.
The evidence suggests that the increased risk of cervical cancer begins to drop as soon as you stop taking the pill. After 10 years the risk is the same as if you had never taken it. The important thing to remember is that regular screening can pick up changes in the cervix before they develop into a cancer. Obviously, screening is now very important for women taking the pill.
Some research suggests that women with partners who have been circumcised are less likely to get cervical cancer. This may be because men who are circumcised are less likely to carry HPV infection. This research took into account different factors relating to sexual behaviour.
You will quite often hear that women who started having sex young or women who have a lot of different sex partners are more likely to get cervical cancer. But really, this is only true because the earlier you start having sex and the more men you have sex with, the more likely you are to pick up an infection with a high risk (cancer causing) human papilloma virus (HPV). And so then you are more at risk of developing cervical cancer.
It is not correct to say that women who get cervical cancer have it because they were promiscuous (slept around). After all, you could have only slept with one man and still caught the virus if he had it. If he's had lots of partners, that will increase your risk, because it indirectly exposes you to possible sexual infections from lots of other people.
Health education may help women reduce their exposure to HPV and so reduce the risk of cervical cancer. Some studies have shown that teaching women about healthy sexual behaviour, such as using condoms, avoiding sex when they are young, learning how to talk to their partner about safe sex and reducing the number of sexual partners, can help them behave in ways that may lower their cervical cancer risk.
There is no evidence at all to say that pregnancy increases the risk of cervical cancer. Abnormalities in the cervix may become more visible during pregnancy and so be more likely to be diagnosed. Some women may have a screening test when they are pregnant. Women who are not up to date with their cervical screening are more likely to be offered a test when they go to the doctor because of their pregnancy. This screening might lead to women being diagnosed with pre cancerous changes or cervical cancer while they are pregnant. But this does not mean that the pregnancy caused the cancer – just that this is when it was picked up.
Women in developing countries have a higher cervical cancer risk. This is partly because developing countries don't have screening. It is also because women in developing countries are more likely to have large families. Women who have had 7 or more children have double the risk of women with only 1 or 2 children. Having your first baby early, before 17, also doubles the risk, compared to having your first baby at 25 or older. This research also took account of HPV infection, and found that HPV infection did not explain the increase in cervical cancer in women who had larger numbers of children.
Other similar research looked at the different types of cervical cancer. They also found a doubling of risk of squamous cell cervical cancer with 3 or more children, compared to no children. But they found that the risk of adenocarcinoma went up by half (50%).
Black women with HPV may have a higher cervical cancer risk than white women with HPV. An American study showed this may be because African American women take longer to clear HPV infection compared to European American women. However we need more studies to confirm any effect of ethnic group.
A study has shown that women with a first degree relative (mother, sister or daughter) diagnosed with adenocarcinoma or squamous cell carcinoma of the cervix have double the risk of developing cervical cancer, compared to women without a family history. But we don’t know whether this is linked to faulty genes, or whether it is due to common lifestyle factors and it is just one study. In some cases it may be that HPV infection is passed on during pregnancy and childbirth.
Around 1 out of 100 cervical cancers in women in the UK (1%) are thought to be linked to occupation. This is due to exposure to a chemical called tetrachloroethylene. This is used in dry cleaning and metal degreasing.
One study has shown that the rate of cervical cancer is higher among women of working age in manual than non manual classes.
It has also been shown that women living in the poorest (most deprived) areas of the UK are more likely to develop cervical cancer than those living in more wealthy areas.
Diethylstilboestrol is also called DES. It is a drug that doctors gave women in the 1940s to 60s to stop them having a miscarriage. The daughters of women who took DES during their pregnancy are more at risk of developing a rare type of cervical cancer called clear cell adenocarcinoma. DES hasn't been used for 40 years and so is becoming less important as a risk factor.
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