A technique whereby X-rays are used to show the structure of the breast and any abnormalities present (see BREASTS; BREASTS, DISEASES OF). It takes about 5–10 minutes to perform and discomfort is minimal. It is an effective way of distinguishing benign from malignant tumours, and can detect tumours that cannot be felt. In a multi-centre study in the US, called The Breast Cancer Detection Demonstration Project and involving nearly 300,000 women in the 40–49 age group, 35 per cent of the tumours found were detected by mammography alone, 13 per cent by physical examination, and 50 per cent by both methods combined.

The optimum frequency of screening is debatable: the American College of Radiologists recommends a baseline mammogram at the age of 40 years, with subsequent mammography at one- to two-year intervals up to the age of 50; thereafter, annual mammography is recommended. In the United Kingdom a less intensive screening programme is in place, with women over 50 being screened every three years. As breast cancer is the commonest malignancy in western women and is increasing in frequency, the importance of screening for this form of cancer may appear obvious but critics point out the risk of false positive results leading to un-necessary anxiety and detection of tumours, which might not have caused the person any problem in later years, leading to possibly unnecessary surgery.