Breast cancer: age-specific growth rates and screening strategies.

In an earlier work, the author and colleagues predicted that the lead time gained by mammographic screening of an asymptomatic, randomly selected population of women was 2 years +/- 0.5 for women aged 35-49 years and 3.5 years +/- 0.5 for those over age 50. At the completion of long-term follow-up of 10,530 women (with a total of 111,087 "person years"), the resultant lead time actually gained seems to be 12-24 months for women aged 35-49 years at entry and 3.5-4 years for older women. Failure to take this lead time into account in the design of controlled trials may well result in failure to decrease mortality due to breast cancer. The results of the present study and those of recent Dutch and Swedish trials suggest that the most effective screening strategy may be annual mammographic and clinical examinations for women aged 40-49 years and biennial examinations thereafter.