A set of investigations aimed at the early detection of breast cancer. It includes self-screening by monthly examination of the breasts, and formal programmes of screening by X-ray mammography in special clinics. In the UK the NHS offers regular mammography examinations to all women between 50 and 70 years of age at 80 special screening units. Younger women are not screened because they have a very low rate of cancer. While it is estimated that screening may reduce cancer rates by 20%, there is a risk of overdiagnosis and overtreatment which remains a source of controversy.