Professor Fidelma Flanagan:

With any screening programme, it boils down to two main principles. First, what is the incidence of the disease in the population? This is a public health initiative to improve mortality by early detection so the first question is what the incidence is, and age is the biggest risk factor. The older one is, the more likely one is going to have breast cancer. For example, for a 30-year-old the incidence of breast cancer is around one in 200 while the incidence of breast cancer for 80-year-old ladies is one in ten. Thus, the biggest risk factor is an increase in age, so that is the background population.

The second principle of screening then is what the test is. The test in this case is the mammogram. It is a good test; it is not a perfect test. It will pick up most cancers but there are some it may not pick up. While it is very sensitive to breast cancer in early detection it is not that specific so in order to pick up a breast cancer one is going to have to take back a certain number of healthy women and subject them to extra tests, such as more X-rays, an ultrasound, a biopsy and even extra surgery. That is a really important harm this screening programme can do to healthy women. The other impact is that in order, for example, to pick up those seven patients with breast cancer out of 1,000, we probably take back about 50 or 60 women and subject them to that. It is well documented that the psychological and anxiety effects associated with calling back women, even if at the end of the day they do not have breast cancer, is very long-lasting. It can last for a year or even two and might have an impact on that woman turning up for her mammogram again in two years' time. Thus there is a huge balance between has this women got breast cancer, how many women do I need to take back and what is the impact on the women who do not have breast cancer but who I do have to take back. That is the balance we are looking at.