Prostate Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit
Summary of First Four Prostate, Lung, Colorectal, and Ovarian Screening Roundsa continued...
After 7 years of follow-up, with vital status known for 98% of men, the incidence of prostate cancer per 10,000 person-years was 116 (2,820 cancers) in the screening group and 95 (2,322 cancers) in the control group (rate ratio, 1.22; 95% CI, 1.16-1.29). The incidence of death per 10,000 person-years was 2.0 (50 deaths) in the screening group and 1.7 (44 deaths) in the control group (rate ratio, 1.13; 95% CI, 0.75-1.70). The data at 10 years were 67% complete and consistent with these overall findings (incidence rate ratio, 1.17; 95% CI, 1.11-1.22 and mortality rate ratio, 1.11; 95% CI, 0.83-1.50). Thus, after 7 to 10 years of follow-up, the rate of death from prostate cancer was very low and did not differ significantly between the two study groups.
At 7 years, the total numbers of deaths (excluding those from prostate, lung, or colorectal cancers) were 2,544 in the screening group and 2,596 in the control group (rate ratio, 0.98; 95% CI, 0.92-1.03); at 10 years, the numbers of such deaths were 3,953 and 4,058, respectively (rate ratio, 0.97; 95% CI, 0.93-1.01). The distribution of the causes of death was similar in the two groups.
The following are several possible explanations for the lack of a reduction in mortality so far in this trial:
- Annual screening with the PSA test using the standard U.S. threshold of 4 ng per mL and DRE to trigger diagnostic evaluation may not be effective.
- The level of screening in the control group could have been substantial enough to dilute any modest effect of annual screening in the screening group.
- Approximately 44% of the men in each study group had undergone one or more PSA tests at baseline, which would have eliminated some cancers detectable on screening from the randomly assigned population; thus, the cumulative death rate from prostate cancer at 10 years in the two groups combined was 25% lower in those who had undergone two or more PSA tests at baseline than in those who had not been tested.
- Potentially, the most important explanation is that improvement in therapy for prostate cancer during the course of the trial probably resulted in fewer prostate-cancer deaths in the two study groups, which blunted any potential benefits of screening.
- The follow-up may not be long enough for benefit from the earlier detection of an increased number of prostate cancers in the screening group to emerge.
- After a PSA finding greater than 4.0 ng/mL, within 1 year only 41% of men underwent prostate biopsy; within 3 years of this finding, only 64% of men underwent prostate biopsy. Such lower biopsy rates, associated with lower prostate cancer detection rates, may have blunted the impact of screening on mortality.