Mammography screening controversies.

Some organizations in the U.S. recommend mammography screening at 1- to 2-year intervals for those aged 40 to 49 and annually from the age of 50. In Canada and Europe, screening mammography is not recommended for women aged 40 to 49, and mammography every 2 to 3 years for women aged 50 to 69. The screening studies in Europe show no evidence of effectiveness of mammography screening in women aged 40 to 49 in the first 8 to 10 years after initiation of screening. Although at 12 years the recent Swedish overview analysis shows a 13% reduction, this is nonsignificant and the confidence intervals are wide. In the National Breast Screening Study (NBSS) in Canada, annual two-view mammography and physical examinations by carefully trained health professionals were given. In women aged 40 to 49 the ratio of proportions of deaths was 1.36 (95% CI 0.84, 2.21). For women aged 50 to 59, the NBSS evaluated the contribution of mammography over and above physical examination. In spite of detecting many more cancers, mammography did not result in a reduction in breast cancer mortality at 7 years (OR 0.97; 95% CI 0.62, 1.52). Although these results suggest the benefit from screening may be less than assumed, for women over 50, biennial screening to age 74 is probably appropriate in population programs, although careful monitoring will be necessary to ensure that the anticipated effect is achieved.