Dr. Peter McKenna:

There are a number of elements to speak to on that and a question underlies all of them.

The question is how can we rely on a test that will miss 20% to 30% of abnormalities. The fact of the matter is it was relied on because it was the best test available. With regard to the reliability of any individual test, depending on which literature one reads, it could fail between 10% and 40% of the time. For one test that is the failure rate. The success of a programme depends not on reading one smear but on going back three years later, three years later again and three or five years later again, depending on the age of the patient. It is a cumulative safety net that goes in under the patient. I agree that one test on its own is okay, but the benefit accumulates the more tests one has.

If we look at the international literature on this, in countries that have advanced screening programmes, many cancers will develop in women who have been appropriately screened. In Sweden, for example, 25% of cancers develop in women who have been appropriately screened and in the UK that figure is higher. To develop a cancer when in a screening programme is not an unusual event.