Cancers detected and induced, and associated risk and benefit, in a breast screening programme.

Current cancer detection rates and dose levels in the UK Breast Screening Programme are used to compare numbers of cancers detected with numbers predicted to be induced by the screening process itself. Numbers of those detected are shown to exceed those induced by a large margin for women aged over 50 years. The associated benefit/risk ratio is also considered. For younger women this margin is progressively reduced but remains positive at least down to age 40 years, and possibly beyond. Women both with and without a family history of breast cancer are considered. Some implications for familial breast screening programmes are discussed. Some caution may be required before annual screening of women below the age of 35 years.