In women who have breast screening, most cancers are found at an early stage when there is a good chance that treatment will be successful. In the UK more than half of the breast cancers found through screening are discovered very early: when they are very small and haven't spread to the lymph nodes close to the breast.

Over 19 million women have had breast screening in the UK since the breast screening programme was set up in 1988. In this time, it has found more than 117,000 cancers.

A report in 2006, by the Advisory Committee on Breast Cancer Screening, showed that screening saved 1,400 lives a year in England. Research by the International Association for Cancer Research has shown that for every 500 women who have breast screening one life will be saved.

Women who take part in breast screening reduce their risk of dying from breast cancer.

In women who have breast screening, any cancer is more likely to be found early. This means that the cancer is likely to be small and more likely to be removed by a lumpectomy (removal of the lump) rather than needing a mastectomy (removal of the whole breast). Approximately 7 out of 10 (70%) women whose breast cancer is diagnosed by screening have breast conserving therapy, compared with 55% of women diagnosed outside the screening programme.