An epidemiological perspective on cancer screening

Abstract

Objective: To provide an epidemiological perspective on cancer screening.

Methods and results: For screening to be applicable as public health policy, the disease has to be an important health problem, there has to be evidence that early detection results in improved outcome, that adequate facilities for diagnosis, therapy, and subsequent management of true and false positives are available, that screening is acceptable to the target groups, and that programs are cost effective in the population. Although it is relatively easy to demonstrate that screening results in earlier detection of cancer, survival is a biassed measure of its effectiveness. The only valid design to study the efficacy of screening is the randomized trial. Cervical cancer screening was introduced before these requirements were recognized. There is, however, good evidence of its effectiveness; the challenge is to make programs cost effective. For breast cancer, studies show little or no evidence of effectiveness of mammography screening in women age 40-49. For women age 50-69, there is good evidence of effectiveness in trials comparing screening with no screening. These support the introduction of population-based programs for this age group. The challenge is to put the research results into practice to ensure cost-effective programs. For colo-rectal cancer, there is some evidence that both screening sigmoidoscopy and the fecal occult blood test will reduce mortality. It is not clear, however, whether programs using either or both these tests will be cost effective. For lung cancer, there is good evidence of no benefit for screening. For ovarian, prostate, mouth, and skin cancer, although early detection has been demonstrated, there is no evidence of reduction in mortality in the target groups; indeed, prostate screening could result in lowering the overall quality of life.

Conclusion: Screening, which offers a fairly rapid return from appropriate investment, should remain part of our armamentarium for cancer control.