Dr. Nóirín Russell:

I would love to expand on that. When we speak about screening programmes, and I will speak specifically to CervicalCheck, we know that when we screen 1,000 women, within them there would be 20 women with a risk factor for developing cervical cancer, and screening with cytology or smear tests would detect 15 from those 20, or 75% of women with that risk factor. Screening with primary HPV will detect 18 from 20 women with that risk factor or 90%. There is no screening test for cervical cancer that detects all women at risk. There will always be women with a screening test that is negative but who will go on to develop a cancer.

As a clinician, I have been in the room with such women and it is devastating to receive that diagnosis. These are women who have done everything right, gone for their screening test and followed up where asked but who still went on to get cancer. That is a really hard diagnosis to get. We know from international literature and the reviews of the CervicalCheck programme that when we look back on the slides for women who were screened and go on to develop cancer, there is a four in ten chance we would see a different result looking back than was seen at the time of screening. That is the reality of what a review is likely to reveal. That is retrospective bias. When we look back on something knowing the outcome, we see things differently and it is not a simple test.

The line between normal and abnormal is not firmly drawn. There is a variety of appearance. Some normal cells look very abnormal and some abnormal cells look very normal. That is the point about looking back.