Mammograms Beginning at Age 40? Mortality Reduced, but Not Conclusively

Screening mammography for women older than 50 is widely recommended based on clear evidence that it reduces breast cancer mortality. In the U.S., most guidelines recommend beginning mammography at age 40, although evidence of net benefit in women this young has been inconclusive.

Between 1991 and 1997, more than 160,000 British women aged 39 to 41 were randomized to receive either annual invitations for screening mammography until age 48 or no intervention. (All British women receive annual invitations for routine screening mammography beginning between ages 50 and 52.) In the intervention group, 81% of women accepted at least one invitation for mammography, with an overall mean of 4.5 examinations per woman. Breast cancer (invasive or in situ) was detected in about 1 in 1000 screening exams. After a mean follow-up of 10.7 years, the relative risk for breast cancer mortality in the intervention group was 0.83 (95% confidence interval, 0.66–1.04); the absolute risk reduction was 0.4 per 1000 women in the screening group. All-cause mortality was similar in the two groups.