Cancer of the cervix can take many years to develop. Before it does, changes occur in the cells of the cervix. These abnormal cells are not cancerous, and are called cervical intra-epithelial neoplasia (CIN). Some doctors call these changes pre-cancerous. This means that the cells might develop into cancer in some women if they are not treated. It is important to know that most women with CIN do not develop cancer.

CIN may also be referred to as dysplasia or dyskaryosis.

Most women have regular cervical screening with a smear test or liquid-based cytology. The screening is designed to find early changes in the cells of the cervix, so that treatment can be given to prevent a cancer from developing. Although the aim of cervical screening is to prevent cancer, it can also sometimes detect a cancer that has already developed, before any symptoms occur.

The smear test or liquid-based cytology are commonly used as routine tests to detect early cell changes (CIN) in the cervix. These tests are used as part of the UK cervical screening programme for women with no symptoms. However, they can sometimes be used to help diagnose a cancer of the cervix.

The smear test Before the test you will be helped into position on the couch. The nurse or doctor then uses an instrument called a speculum to hold the vaginal walls open. They then gently scrape a sample of the cells from the cervix (using a small spatula) and spread this onto a glass slide. Sometimes a small brush may be used instead to collect the cervical cells. The sample is sent to a laboratory to be examined under a microscope, to look for any abnormalities. A smear test may sometimes be slightly uncomfortable, but it should only take a few minutes.

Liquid-based cytology This is another method of collecting cells from the cervix. The sample is taken in a similar way to the smear, but uses a special brush that gently takes cells from the cervix. The cells are put into a liquid and sent to a laboratory. In the laboratory the cells are put on a glass slide and examined under a microscope.

CIN is usually the result of a virus infection: the human papillomavirus (HPV). HPV is a very common virus that can affect the cells of the cervix. It is mainly passed on during sexual intercourse. Most women who have had sexual intercourse will have the virus at some time in their life. However, in many women their immune system will get rid of the virus and they won't even know they had it.

There are more than 100 types of HPV and each type is identified by a number (eg HPV 16). Some types of the virus can cause genital warts, and other types can cause CIN in the cells of the cervix. The CIN usually clears up once the immune system has got rid of the virus. In some women the virus stays for a number of years and in a few of these women the CIN will develop into cancer if it is not treated.

The type of HPV can affect whether CIN develops or not. Only certain types, such as 16, 18, 31 and 33 (known as ‘high risk’ types) seem to be associated with the development of CIN.

Recently several research trials have looked at using vaccines to prevent HPV infection. The results seem to show that in future, it will be possible to vaccinate young women against the high-risk types of HPV and so prevent most cases of cervical cancer.

Sometimes the abnormality found by a cervical screening test is mild (CIN 1). In this situation the cells may go back to normal on their own, so for CIN 1 no treatment is given. The test should be repeated in a few months.

Women who have a few abnormal screening tests, or moderate or severe cell changes (CIN 2 or 3), are referred to a hospital colposcopy unit. Only a small number of women with CIN will develop cervical cancer, but it is important for a doctor to check the abnormal cells.

CIN that might develop into cancer can be treated in various ways. The aim of any treatment is to remove or destroy all of the affected cells. This can be done using surgery, where the affected area of the cervix is removed by large loop excision (LLETZ) or cone biopsy. Instead, the affected areas can be destroyed by laser therapy, or using heat (cold coagulation). These procedures are usually carried out in an outpatient clinic and may be done by doctors or specialist nurses.

For detailed information about CIN and its treatment, see our section on cervical screening.