Prostate Cancer Screening Did Not Reduce Prostate Cancer Deaths in U.S. Trial
The Bottom Line
Initial results from a large randomized trial conducted in the United States suggest that prostate cancer screening with the digital rectal examination (DRE) and prostate specific antigen (PSA) tests may not reduce the number of deaths from prostate cancer.
The Whole Story
The goal of cancer screening is to find cancer early, before there are symptoms and when the disease may be most treatable. A truly effective cancer screening test, therefore, should help reduce the number of deaths from the cancer it aims to detect.
Currently, two tests are widely used to screen for prostate cancer, DRE and the PSA test. Although both tests can help doctors find prostate cancer at an early stage, it is not clear whether earlier detection and treatment of prostate cancer will help reduce the number of deaths from this disease.
To address this question, the National Cancer Institute included an evaluation of DRE and PSA testing in its Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, which began in 1993. In the trial, 76,693 men were randomly assigned to annual prostate cancer screening (38,343 men) or to usual care (38,350 men). The men in the usual-care group received no recommendations for or against prostate cancer screening. The men in the screening group received a DRE and a PSA test upon joining the trial; thereafter, they received an annual DRE for 3 years and an annual PSA test for 5 years. When the initial results of the trial were reported, the median length of follow-up was 11.5 years. At that time, complete information was available for 98 percent of the men through 7 years of follow-up. Complete information was also available for 67 percent of the men through 10 years of follow-up (not all trial participants had been enrolled in the study for 10 years).
The trial's initial results revealed the following:
- At 7 years (or, 2 years after the end of screening), 2,820 prostate cancers had been diagnosed in the screening group compared with 2,322 prostate cancers in the usual-care group, meaning 22 percent more prostate cancers were diagnosed in screened men. This excess of prostate cancers persisted among men with complete information through 10 years of follow-up; among these men, 17 percent more prostate cancers were diagnosed in the screening group than in the usual-care group.
- Among men with complete information though 10 years of follow-up, more than 90 percent of those who developed prostate cancer, regardless of assigned group, were diagnosed with relatively early stage disease (clinical stage II); the numbers of later-stage cases (clinical stages III and IV) were similar in the two groups.
- Men in both groups who were diagnosed with prostate cancer at the same stage received similar treatments for their disease.
- At 7 years, 50 deaths due to prostate cancer had been observed in the screening group compared with 44 prostate cancer deaths in the usual-care group. Through 10 years of follow-up, 92 prostate cancer deaths were observed in the screening group compared with 82 prostate cancer deaths in the usual-care group. These differences were not statistically significant. The results indicate, therefore, that annual prostate cancer screening may not reduce the number of deaths from this disease.
At the same time the PLCO trial results were reported, initial results from another large trial, the European Randomized Study of Screening for Prostate Cancer (ERSPC), were published. In ERSPC, as in the PLCO, more prostate cancers (39 percent more) were diagnosed in the screening group than in the comparison (control) group. In contrast with the PLCO, prostate cancer screening in ERSPC was associated with a 20 percent reduction in prostate cancer deaths. This benefit, however, was associated with high costs: to prevent one death from prostate cancer, 1,410 men would have to be screened and 48 additional cases of prostate cancer would have to be treated. This means that many men would undergo treatment, and they would experience the serious side effects of treatment (including urinary incontinence and impotence), for cancers that would never threaten their lives.
Follow-up will continue for several more years in both trials. It is unclear at this point whether the initial findings will persist with longer follow-up. Given the uncertainty about the benefits of current prostate cancer screening tests, NCI is sponsoring research aimed at the development of new methods to allow the detection of prostate cancer as early as possible in the disease process.
More summaries of selected scientific advances from NCI-supported research are available at http://www.cancer.gov/aboutnci/servingpeople/advances.