Breast cancer screening: a 35-year perspective.

Screening for breast cancer has been evaluated by 9 randomized trials over 5 decades and recommended by major guideline groups for more than 3 decades. Successes and lessons for cancer screening from this history include development of scientific methods to evaluate screening, by the Canadian Task Force on the Periodic Health Examination and the U.S. Preventive Services Task Force; the importance of randomized trials in the past, and the increasing need to develop new methods to evaluate cancer screening in the future; the challenge of assessing new technologies that are replacing originally evaluated screening tests; the need to measure false-positive screening test results and the difficulty in reducing their frequency; the unexpected emergence of overdiagnosis due to cancer screening; the difficulty in stratifying individuals according to breast cancer risk; women's fear of breast cancer and the public outrage over changing guidelines for breast cancer screening; the need for population scientists to better communicate with the public if evidence-based recommendations are to be heeded by clinicians, patients, and insurers; new developments in the primary prevention of cancers; and the interaction between improved treatment and screening, which, over time, and together with primary prevention, may decrease the need for cancer screening.