Screening: assessment of current studies

Abstract

Background: A major issue in decisions regarding screening women for breast cancer concerns ages of coverage, in particular, whether routine mass screening programs with mammography should cover women aged 40-49. Interpretation of results of studies on this question is affected by differences in design, adequacy of sample size, quality of mammography, period of follow-up, and other methodologic and content issues.

Methods: Experience in eight randomized controlled trials (RCTs) conducted over the past 30 years in the United States, Europe, and Canada were assessed, and problems influencing their conclusions were considered.

Results: The age groups studied in these RCTs varied, from 40-64 in the Health Insurance Plan (HIP) study to 40-74 in the Swedish two-country trials. In addition, they differed in periodicity and modalities of screening, with the HIP and the Canadian National Breast Screening Study providing annual examinations with mammography and clinical breast examination, and most of the other trials scheduling longer intervals between examinations with mammography alone. Great consistency is found, however, in the results for women aged 50-69, as all of these studies showed a reduction in breast cancer mortality in this age group, suggesting about a 30% decrease. For women aged 40-49, the studies showed no benefit 5-7 years after entry and an uncertain benefit 10-12 years after entry, and only one study offered information on long term effects. Additional follow-up is needed. Adequate data are not available for women 70 and older.

Conclusion: Public health policy on mass screening with mammography for women aged 40-49 is questionable. At this time, the emphasis should be on physicians advising women about the uncertainty of the benefits of routine mammography when referrals are being considered.