What is the problem and what is known about it so far?

Prostate cancer occurs frequently, and the screening test does a good job of identifying men with the disease. Some cancer cases respond well to treatment, but others do not need treatment because the cancer does not respond or because it grows very slowly. It is difficult to separate cancer that responds from other cancer, so it is difficult to know when to treat and when not to treat. In this situation, screening involves tradeoffs. If screening is not done, more men will fail to get treatment that might prevent premature death because their cancer will go undetected until after it has spread. If screening is done, more men will get treatment that cannot help them, and some of them will have lower quality of life due to the treatment.

Why did the researchers do this particular study?

Two clinical trials—one in Europe and the other in the United States—provide the best information about whether screening lowers the risk for death due to prostate cancer. The European study found that men who were invited to be screened had fewer prostate cancer deaths than men who were not invited, but the American study found similar numbers of prostate cancer deaths in the 2 groups. The researchers of the current study wanted to figure out whether the results of the 2 trials were as different as they seemed.

Who was studied?

Both trials studied men aged 55 years or older, and both randomly invited some men to be screened but not others.

How was the study done?

In the 2 original studies, some men who were invited to be screened did not get screened, and some men who were not invited were screened anyway. These studies used traditional methods to compare the risk for death due to prostate cancer in men invited to have screening with the risk for death in men who were not invited to have screening. In contrast, the current study used a different approach to examine how the actual amount of screening in each group—regardless of whether men were invited to have screening—affected the risk for death due to prostate cancer.

What did the researchers find?

The 2 trials had remarkably similar results when the amount of screening actually received in each group was accounted for. Screening lowered the risk for prostate cancer death by 25% to 32% in men who were invited to have screening in the 2 trials compared with those who were not screened.

What were the limitations of the study?

The researchers used a simplified summary measure of how much screening was actually received in each trial group.

What are the implications of the study?

The European and American trials agree that screening lowers the risk for death due to prostate cancer compared with no screening.

中文翻译：

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两项试验中筛查对前列腺癌死亡的不同影响

问题是什么？到目前为止我们知道什么？

前列腺癌经常发生，筛查测试可以很好地识别患有这种疾病的男性。一些癌症病例对治疗反应良好，但其他癌症病例不需要治疗，因为癌症没有反应或生长非常缓慢。很难将有反应的癌症与其他癌症区分开来，因此很难知道何时治疗，何时不治疗。在这种情况下，筛选涉及权衡。如果不进行筛查，更多的男性将无法获得可能预防过早死亡的治疗，因为他们的癌症直到扩散后才会被发现。如果进行筛查，更多的男性会得到无法帮助他们的治疗，其中一些人会因为治疗而生活质量下降。

研究人员为什么要进行这项特殊研究？

两项临床试验——一项在欧洲，另一项在美国——提供了关于筛查是否能降低前列腺癌死亡风险的最佳信息。欧洲研究发现，受邀接受筛查的男性前列腺癌死亡人数少于未受邀接受筛查的男性，但美国研究发现两组的前列腺癌死亡人数相似。当前研究的研究人员想弄清楚这两项试验的结果是否像看起来那样不同。

研究了谁？

两项试验都研究了 55 岁或以上的男性，并且都随机邀请了一些男性进行筛查，而不是其他人。

研究是如何进行的？

在 2 项原始研究中，一些被邀请接受筛查的男性没有接受筛查，而一些未被邀请的男性无论如何都接受了筛查。这些研究使用传统方法来比较受邀进行筛查的男性因前列腺癌而死亡的风险与未受邀进行筛查的男性的死亡风险。相比之下，目前的研究使用不同的方法来检查每组的实际筛查量（无论是否邀请男性进行筛查）如何影响因前列腺癌而死亡的风险。

研究人员发现了什么？

当考虑到每组实际接受的筛查量时，这两项试验的结果非常相似。与未接受筛查的男性相比，筛查使在 2 项试验中被邀请接受筛查的男性前列腺癌死亡风险降低了 25% 至 32%。

该研究的局限性是什么？

研究人员对每个试验组实际接受了多少筛查进行了简化的汇总测量。

这项研究的意义是什么？

欧洲和美国的试验一致认为，与不进行筛查相比，筛查可以降低因前列腺癌而死亡的风险。