Women who have previously been treated for abnormal cells on the cervix are at an increased risk of developing and dying from cervical cancer and vaginal cancer later in life, the results of a new study indicate.

The use of smear tests to detect pre-cancerous cells in the cervix (the neck of the womb) is a major medical success story. If detected, these cells can be removed before they have a chance to become cancerous.

The current internationally recognised system for classifying smear test results is called the CIN classification (Cervical Intraepithelial Neoplasia). This is simply a grading system that allows a laboratory technician to classify varying degrees of abnormality in the cells.

There are three grades of CIN - I, II and III. CIN I is the least severe category of change and CIN III is the most severe.

Swedish researchers decided to look into how ageing affects the risk of death from cervical cancer following treatment of CIN III.

They analysed data on over 150,000 women who had been treated for CIN III in the past and found that they had an increased risk of developing invasive cervical cancer as they grew older. They also had an increased risk of invasive vaginal cancer. This risk appeared to accelerate after the age of 60 and again after the age of 75.

The researchers noted that the more recent a woman was treated for CIN III, the higher the risk of cancer.

The risk of death from these cancers was also significantly higher than for the general population. Thirty years after treatment for CIN III, the risk of death from these cancers was more than double that of the general population.

However, the researchers emphasised that after treatment for CIN III, patients ‘are well protected from cervical cancer'. They said that only a minority will develop and die from these diseases and noted that women with a CIN III history will most likely ‘have been followed up more closely than other women of the same age' and are therefore easily identifiable.

They concluded that CIN III treatment is extremely beneficial for women, however the risk of developing or dying from cervical or vaginal cancer is strongly increased among such women after the age of 60 compared to the general population.

They added that women previously treated for CIN III ‘should be followed up in old age'.

Details of these findings are published in the British Medical Journal.