In almost all cases, cervical cancer is the result of a change in cell DNA caused by the human papilloma virus (HPV).
Cancer begins with a change in the structure of the DNA that's present in all human cells. DNA provides the cells with a basic set of instructions, including when to grow and reproduce.
A change in the DNA's structure is known as a mutation. It can alter the instructions that control cell growth, which means the cells continue growing instead of stopping when they should. If the cells reproduce uncontrollably, they produce a lump of tissue called a tumour.
Human papilloma virus (HPV)
More than 99% of cervical cancer cases occur in women who have been previously infected with HPV. HPV is a group of viruses, rather than a single virus. There are more than 100 different types.
HPV is spread during sexual intercourse and other types of sexual activity (such as skin-to-skin contact of the genital areas, or using sex toys) and is thought to be very common. It's estimated that 1 in 3 women will develop a HPV infection within two years of starting to have regular sex, and about 4 in 5 women will develop the infection at some point in their lives.
Some types of HPV don't cause any noticeable symptoms and the infection will pass without treatment. Other types of HPV can cause genital warts, although these types aren't linked to an increased risk of causing cervical cancer.
About 15 types of HPV are considered high-risk for cervical cancer. The two types known to have the highest risk are HPV 16 and HPV 18, which cause about 7 out of every 10 cervical cancers.
High-risk types of HPV are thought to contain genetic material that can be passed into the cells of the cervix. This material begins to disrupt the normal workings of the cells, which can eventually cause them to reproduce uncontrollably, leading to the growth of a cancerous tumour.
As most types of HPV don't cause any symptoms, you or your partner could have the virus for months or years without knowing it.
See preventing cervical cancer for more information about reducing your chances of developing an HPV infection.
Cervical intraepithelial neoplasia (CIN)
Cancer of the cervix usually takes many years to develop. Before it does, the cells in the cervix often show changes known as cervical intraepithelial neoplasia (CIN) or, less commonly, cervical glandular intraepithelial neoplasia (CGIN).
CIN and CGIN are pre-cancerous conditions. Pre-cancerous conditions don't pose an immediate threat to a person's health, but they can potentially develop into cancer in the future.
However, even if you develop CIN or CGIN, the chances of it developing into cervical cancer are very small, and if the changes are discovered during cervical screening, treatment is highly successful.
The progression from becoming infected with HPV to developing CIN or CGIN and then developing cervical cancer is very slow, often taking 10 to 20 years.
Read more about cervical screening results.
The fact that HPV infection is very common but cervical cancer is relatively uncommon suggests that only a very small proportion of women are vulnerable to the effects of an HPV infection. There appear to be additional risk factors that affect a woman's chance of developing cervical cancer. These include:
- smoking – women who smoke are twice as likely to develop cervical cancer than women who don't; this may be caused by the harmful effects of chemicals found in tobacco on the cells of the cervix
- having a weakened immune system – this can occur as a result of taking certain medications, such as immunosuppressants, which are used to stop the body rejecting donated organs, or as a result of a condition such as HIV or AIDS
- taking the oral contraceptive pill for more than five years – women who take the pill are thought to have twice the risk of developing cervical cancer than those who don't, although it's not clear why
- having children (the more children you have, the greater your risk) – women who have two children have twice the risk of getting cervical cancer compared with women who don't have any children
The reason for the link between cervical cancer and childbirth is unclear. One theory is that the hormonal changes that occur during pregnancy may make the cervix more vulnerable to the effects of HPV.
The spread of cervical cancer
If cervical cancer is undiagnosed and untreated, it will slowly spread out of the cervix and into the surrounding tissue and organs. The cancer can spread down to the vagina and the surrounding muscles that support the bones of the pelvis. Alternatively, it can spread upwards, blocking the tube that runs from your kidneys to your bladder (ureters).
The cancer can then spread into your bladder, rectum (back passage) and eventually into your liver, bones and lungs. Cancerous cells can also spread through your lymphatic system. The lymphatic system is a series of nodes (glands) and channels spread throughout your body in a similar way to the blood circulation system.
The lymph nodes produce many of the specialised cells needed by your immune system (the body's natural defence against infection and illness). If you have an infection, the nodes in your neck or under your armpits can become swollen.
In some cases of early cervical cancer, the lymph nodes close to the cervix contain cancerous cells. In some cases of advanced cervical cancer, lymph nodes in the chest and abdomen can be affected.