The costs and benefits of breast cancer screening.

The costs and benefits of breast cancer screening can be placed in the framework usually used for sensitivity and specificity. All those screened incur the costs associated with the test. In addition, only the segment of the true positives who, in the absence of screening, would die of their disease but with screening will survive to die of another cause truly benefit; all other true positives acquire lead time without benefit. In the Canadian National Breast Screening Study, simpler treatment of screen-detected cancer was not achieved. The true negatives benefited from reassurance, but the majority were not at risk of breast cancer anyway. The false negatives were disadvantaged from false reassurance, but in practice the percentage is low, and the consequences are not dire. There are major costs associated with the false positive state, including anxiety, unnecessary biopsies, and residual scarring; major endeavors are justified to reduce them and improve the specificity of screening. In practice, with no benefit demonstrated for women 40-49 years of age, the costs are too great to justify continuation of screening this age group merely in the hope that benefits will eventually be demonstrated. For women older than 50, the degree of benefit may have been overestimated, especially in an era when improvements in therapy affect screen-detected and nonscreen-detected cases alike. We may have overestimated the benefit-cost ratio of screening this age group also; thus, careful monitoring of the outcome of ongoing programs over the next few years is essential.