Prorok P C, Connor R J, Baker S G
Division of Cancer Prevention and Control, National Cancer Institute, Bethesda, Maryland.
Urol Clin North Am. 1990 Nov;17(4):699-708.
The goal of cancer screening is the early detection and treatment of disease, with a consequent reduction in the mortality rate. Evaluation of whether a particular screening program can achieve this goal is a difficult task. Two components of the screening process must be assessed. The first is the ability of the screening test to detect cancer early while minimizing the number of false-positive results. In this regard, the specificity of the test ordinarily must be very high, approaching 99%. No screening test for prostate cancer has yet been reported to have a specificity this high, indicating that any prostate cancer screening program using currently available tests will have to deal with the problem of a large number of false-positive findings. To evaluate the overall impact of a screening program, the best procedure is the randomized controlled trial with cancer-specific mortality as the endpoint. This endpoint is used because it avoids the lead time and length biases inherent in other outcome variables such as stage shift and case survival. The screening randomized controlled trial must be carefully planned and implemented, because it is lengthier and more costly than the usual therapy trial because of differences in study populations, trial design relative to the planned population intervention, and the extent of knowledge of disease natural history. A further important component of screening evaluation is cost. The decision to implement or continue a screening program can be aided by using cost-effectiveness analysis, which bases a decision on the ranking of cost-to-benefit ratios for the various programs contending for limited funds. Screening cost includes the cost of the test, the cost of side effects of the test, and the costs of biopsy and treatment, while screening benefit can be measured in terms of lives saved, life years saved, or quality-adjusted life years.
癌症筛查的目标是早期发现并治疗疾病，从而降低死亡率。评估某个特定的筛查项目是否能够实现这一目标是一项艰巨的任务。筛查过程的两个组成部分必须加以评估。第一个是筛查测试在将假阳性结果数量降至最低的同时早期检测出癌症的能力。在这方面，该测试的特异性通常必须非常高，接近99%。尚无报告称任何前列腺癌筛查测试的特异性能达到如此之高，这表明任何使用现有测试的前列腺癌筛查项目都必须应对大量假阳性结果的问题。为了评估筛查项目的总体影响，最佳方法是以癌症特异性死亡率为终点的随机对照试验。使用这个终点是因为它避免了其他结局变量（如分期转变和病例存活）中固有的领先时间偏倚和长度偏倚。筛查随机对照试验必须精心策划和实施，因为由于研究人群、相对于计划人群干预的试验设计以及疾病自然史的了解程度等方面的差异，它比常规治疗试验耗时更长且成本更高。筛查评估的另一个重要组成部分是成本。使用成本效益分析有助于做出实施或继续筛查项目的决策，该分析基于对争夺有限资金的各个项目的成本效益比进行排序来做出决策。筛查成本包括测试成本、测试副作用成本以及活检和治疗成本，而筛查效益可以用挽救的生命数量、挽救的生命年数或质量调整生命年数来衡量。
