Mammographic screening: efficacy and guidelines.

Over the past year, concerns regarding breast cancer screening guidelines and the benefits of mammography have been raised. These concerns were fueled by a leak of information from the Canadian National Breast Screening study that suggested first an increase in mortality in women aged 40 to 49 years and then, after further investigation, no change in mortality for women screened with mammography as compared with those who relied on physical examination. No benefit from the addition of mammography to physical examination was reported for women aged 50 to 59 years. Published data demonstrate poor mammographic images in the first 3 years of the study. Direct evidence of benefit in women aged 40 to 49 years is available only in the Health Insurance Plan trial in which two-view mammography plus physical examination resulted in a delayed reduction in mortality equal to that in older women. The other trials, except for the Canadian trial, used less sensitive protocols and frequently used single-view mammography at 2- or 3-year intervals. Evidence from the Breast Cancer Detection Demonstration Project suggested benefit in screening women aged 40 years or older with annual mammography and physical examination. This paper reviews 11-year results from the Swedish two-county study and the results of other studies and discusses factors related to frequency, sensitivity, and lead-time.