1. A woman born today has about a 1 in 8 chance of being diagnosed with breast cancer at some time during her life. On the other hand, there is an 87.6% chance that she will never have breast cancer.
2. Breast cancer risk is affected by a number of known factors such as gender, genes and ageing. Four out of five breast cancers are found in women over fifty and for this reason, all women aged 50 - 70 in the UK are invited to attend a breast cancer screening, once every three years.
3. In theory, early detection and early treatment should improve outcomes, but although mammography screening is associated with a modest reduction in breast cancer mortality, the benefit of screening has to be balanced against the potential to do harm.
4. UK research shows that for every breast cancer death that is prevented by screening, 180 women need to be screened and of those women, three will be unnecessarily diagnosed and treated.
5. A US meta analysis of Medline studies of breast cancer screening carried out between 1960-2014 determined that for every 10,000 women aged 50 to 59, ten lives are saved. Overall, they found that screening is associated with a 19% reduction in mortality.
6. But the same study also estimates that there is about a 19% chance that breast cancer will be overdiagnosed and unnecessarily treated.
7. The reason this happens is because breast cancer screening detects carcinoma in situ (CIS), but less than half of all cases of CIS will progress to breast cancer.
8. However, practically all women diagnosed with CIS are treated as if the condition would progress to invasive cancer, which leads to considerable over treatment.
9. Currently it is not possible to distinguish cancers that lead to death from cancers that are unlikely to progress, so neither a woman, nor her doctor can know whether a screen-detected cancer is an 'overdiagnosed' case or not.
10. Women who participate in annual breast cancer screening can anticipate that they will have at least one false-positive finding over a ten year period.