Value of mammographic screening: assessment of studies and opinion.

The purpose of mammographic screening is to improve patient survival by detecting cancer at an earlier, more curable stage than is possible with physical examination. Three major studies have been used to assess the effect of mass screening on the survival rates and mortality for patients with breast cancer: the Breast Cancer Detection Demonstration Project, the Health Insurance Plan study, and the study conducted by the Swedish National Board of Health and Welfare. The author reviews these studies, describes statistical biases (lead time, length time, patient self-selection, and overdiagnosis) to be considered in study design and analysis, and discusses briefly risks versus benefits of mammography.