Cervical cancer is the third most common female cancer in the UK, after breast and ovarian cancer. Fortunately the cervix is small enough, and accessible enough so that a doctor or nurse can fairly painlessly take a good smear of cells from it to look at under the microscope, and check if there are any cancerous or pre-cancerous cells present.

The most common abnormal findings on cervical smears are pre-cancerous changes rather than cancer. These range from very early changes (CIN1) which often revert to normal on their own, to higher grade changes such as CIN3 which need treatment to prevent them going on to a cancer. This is the aim of a smear - to pick up and treat these changes before they turn into a cancer.

Around 10-30% of smears will be reported as being normal when they are not (a false negative). This may happen because the person reading the smear does not pick up a few abnormal cells among many thousands of normal cells, or because an inadequate sample of cells was gained from the smear. If this is the case the women will be asked to return so that another smear can be taken to get more cells.

However, most false negatives are because very early changes are missed. Missing a higher grade abnormality is much less common. If a women has regular cervical smears it is unlikely that a significant abnormality will be continue to be missed over time and because it can take many years for cervical cancer to develop, most abnormalities will eventually be picked up before cancer develops. Despite the problems with false negatives the risk of cervical cancer is reduced by over 90% if a women has regular cervical screening.

As with all cancers, it isn't fully known why some people develop cervical cancer rather than others. There are some factors that are known to increase the risk of this cancer. These include starting regular sexual intercourse at an early age, having many different sexual partners, and having many children. The presence of a wart virus (HPV) in the cervix increases the risk of cervical cancer, as does smoking. Using barrier methods of contraception (i.e. condoms or a diaphragm) helps to protect against cervical cancer. It is important to realise however, that even if you have all the risk factors, you still have only a small chance of developing pre-cancerous changes in the cervix, and an even smaller chance of getting cervical cancer.