What causes cervical cancer?

Cervical cancer is caused by infection with the human papillomavirus (HPV), which can lead to abnormal cell changes and, over time, cancer. HPV is spread by sexual contact and is very common. Many types of HPV are cleared by the body's immune system. However, some women who have had HPV can go on to develop cervical cancer.

How to prevent cervical cancer?

Preventive measures for cervical cancer include: Having regular cervical smears, so abnormalities can be detected and treated early. The HPV vaccine helps prevent infection with the most common types of  HPV (vaccine is most effective if given before the onset of sexual activity). Using condoms can help to reduce the spread of HPV infection, though condoms are not a complete protection from HPV. Risk factors for cervical cancer include having multiple sexual partners, and smoking.

Different types of HPV

There are over 100 types of human papillomavirus (HPV), and more than 40 of these are known to infect the genital skin of both men and women. Of these 40 types, some can cause genital warts while infection with other types in women can lead to changes in cells of the cervix. These cervical cell changes can, over many years, result in pre-cancerous cell types. These are the cells that cervical screening programmes (smear tests) aim to detect, allowing women to get treatment before the cells become cancerous.

HPV and sexual activity

HPV is the most common sexually transmitted infection. Studies of women have found three out of four sexually active women (75%) have been or will be infected with HPV during their lifetime. One US study has estimated that about half of all sexually active young men and women will acquire an HPV infection within five years of first having sexual intercourse. The rates of genital HPV infection are thought to be directly related to sexual activity. The particular risk for any individual is linked to the number of sexual partners.

HPV infections are usually cleared from the body (over approximately 12-30 months) without further problems, but if not cleared, some progress to cervical and other female genital cancers, and to anal cancers and genital warts in both men and women.

Prevention of HPV infection

Safe sexual behaviour will reduce the risk of sexually transmitted infections in general (see our Sexual Health centre for more information). If you do not have a regular long-term sexual partner, you or your partner should always use a condom when having sex, to prevent a number of possible infections. HPV is a very common virus, and studies show that condom use offers only partial protection against it.

Vaccination available

A recently available vaccine (Gardasil) is highly effective against the four most important types of HPV (types 6, 11, 16 and 18). HPV types 16 and 18 cause about 70% of high-grade pre-cancerous changes and cervical cancers. HPV types 6 and 11 cause some low-grade pre-cancerous changes and 90% of genital warts.

The vaccine prevents future infection, but it does not cure an existing infection. However, even if you have been sexually active, and have already been infected with one HPV type contained in the vaccine, the vaccine still provides 95% to 100% protection against the other three types in the vaccine. The vaccine may also reduce the likelihood that the existing HPV infection progresses to a pre-cancerous change, although this is still being studied. (See further below for information on the HPV vaccination programme.)

A second HPV vaccine - Cervarix - offers protection against HPV types 16 and 18. Cervarix is not funded in New Zealand. Both vaccines have been extensively studied and have shown excellent safety.

Cervical screening still a must

It should be remembered these HPV virus types are responsible for most, but not all, of the HPV types that can lead to cervical cancer. So routine cervical screening will still be recommended. Also, screening is necessary because of the possible effects of persistent HPV infection that may have occured before vaccination.

Vaccine protection expected to be long lasting

Studies are ongoing to determine the likely length of HPV vaccine protection and whether booster shots will be needed in later years. The New Zealand Ministry of Health website (www.cervicalcancervaccine.govt.nz/) reports that, so far, protection from HPV infection remains high five years after immunisation (with the full course of 3 doses), and that protection is expected to be long lasting.

Quick facts about human papillomavirus (HPV)

• HPV is the most common sexually transmitted infection (STI) worldwide
• Up to three-quarters of sexually active adults will be infected with HPV during their lifetime
• The majority of HPV infections occur without any symptoms, so you do not know you have an infection
• Most HPV infections are cleared by the immune system within 12-30 months
• Long term HPV infection can cause changes to the cells of the cervix, cervical cancer (taking up to 20 years) or genital warts
• The types of HPV that cause cervical cancer are different from the types that cause genital warts
• Over 99% of cervical cancers are caused by HPV infection
• Condom use does not fully protect against HPV, but condom use is still recommended to protect against other STIs.

Quick facts about the HPV vaccine (Gardasil)

• The vaccine prevents infection (but it does not cure existing infection), so it is most useful if given before sexual activity begins
• The vaccine can be used in girls and women aged 9-45 years and males aged 9-15 years
• The vaccine offers 95% to 100% protection against the main types of human papillomavirus (HPV 6, 11, 16 and 18)
• These types account for about 70% of cervical cancers and high-grade pre-cancers, and 90% of genital warts
• If you have been infected with one HPV type, the vaccine still offers high levels of protection against the other HPV types contained in the vaccine
• There is no routinely available test to detect current or previous infection with HPV
• The vaccine is given in three doses (by injection) over a six-month period (0, 2 and 6 months).

Free HPV immunisation programme

The HPV immunisation progamme was introduced to New Zealand in 2008, and the funded vaccine is Gardasil.

Girls in school year 8 (age 12 years)
From 2011 onwards, the Gardasil vaccine is offered to girls in school year 8 (age 12 years), as part of the National Immunisation Schedule. If a school is not participating in the programme, the vaccine can also be obtained through GPs and health centres. Gardasil is given as a course of three injections, over a six-month period.

Females aged 12-20 years - start before 20th birthday
The funded vaccine is also available for females from age 12 years to 20 years, but they must have begun the course of injections before their 20th birthday.

Females born in 1990 or 1991: 31 Dec 2011 deadline
When the programme was introduced in September 2008, it was originally offered to young women born in 1990 or 1991. To be eligible for the funded vaccination programme, young women who were born in 1990 or 1991 have until 31 December 2011 to start the course.

Males 9-15, and females over 20 years [not funded]
Gardasil is approved for use in New Zealand for females aged 9-45 years and males aged 9-15 years. Males, and females over 20 years, can pay to have the vaccine (discuss this option with your doctor). A second vaccine, Cervarix, is also approved for use in New Zealand (but is not funded for any age groups).

Is the vaccine suitable for everyone?

Some people are not recommended to have the HPV vaccine. These include:

• people who have a severe allergic reaction (anaphylaxis) to any part of the vaccine, including yeast
• pregnant women
• people who have a bleeding disorder or immune condition should seek medical advice before taking the vaccine.

More information on the vaccine is available from the Immunisation Advisory Centre (see details under Further Information and Support below), and from the Ministry of Health website www.cervicalcancervaccine.govt.nz/

Smoking also a risk factor

As cervical cancer is the second most common cause of cancer death in women on a worldwide basis, the HPV vaccine represents a significant advance in preventive health. It is also important to remember that smoking is related to increased development of abnormal cells in the cervix, so by quitting smoking you remove an additional important risk factor.

Procedures to treat cell changes

For women who discover they have early pre-cancerous changes to the cells of the cervix, there are some commonly used surgical procedures that can prevent progression to cervical cancer. These include colposcopy, cone biopsy and loop electrosurgical excision procedure (LEEP).

Related topics

HPV vaccine - Frequently Asked Questions and Cervical screening and Childhood immunisation

Original material provided by everybody. Updated July 2011.