Screening Does Not Reduce Prostate Cancer Deaths
A 20-year study published yesterday in the British Medical Journal (BMJ) found screening does not significantly reduce prostate cancer deaths. Screening does increase the risk of over detection and over treatment.
Prostate cancer is one of the most common cancers among men worldwide. According to the National Cancer Institute, there were 217,730 new cases and 32,050 deaths from prostate cancer reported in the United States in 2010.
Screening is widely used in many countries, but remains controversial because experts can't agree whether the benefits outweigh the potential harms and costs of over diagnosis and over treatment of healthy men.
The 20-year study began in 1987 as a randomized controlled trial on screening for prostate cancer in Norrköping, Sweden. The National Population Register was used to identify 9,026 men aged 50-69 years. From this population, 1,494 men were randomly selected for screening every third year from 1987 to 1996. The remaining 7,532 men acted as controls.
As the study was started before prostate specific antigen (PSA) testing was established as a method of screening, the first two screenings involved only digital rectal examination (DRE). From 1993 DRE was combined with PSA testing. On the fourth occasion (1996), only men aged 69 or under at the time of the investigation were invited.
All men with cancer diagnosed up to December 31, 1999 were included in the analysis. Survival was followed until December 31, 2008.
The main outcome measure was the prostate cancer specific death risk ratio. The study was designed to detect a plausible reduction of prostate cancer specific mortality within 20 years from the start of the study from 1.5% to 1.0% in the screening group.
The researchers note, “A total of 1050 patients in the screening group would be required to detect this difference (80% power, two sided 5% significance level). To allow for non-compliance in the screening group and contamination in the control group, 1400 men were included in the screening group.”
The researchers noted there were 85 cases (5.7%) of prostate cancer diagnosed in the screened group and 292 (3.9%) in the control group. The tumors in the screening group were smaller and more often localized than in the control group, 56.5% vs 26.7% respectively.
The rates of non-localized tumors were not significantly different between the two groups, 37/1494 (2.5%) vs 213/7532 (2.8%) respectively.
Analysis did not show significantly longer survival or overall survival for men with prostate cancer in the screened group compared with the control group.
The prostate cancer specific mortality was 30/85 (35%) for men with prostate cancer diagnosed in the screening group and 130/292 (45%) for men with prostate cancer diagnosed in the control group.
The overall mortality for men with prostate cancer was 69/85 (81%) in the screening group and 252/292 (86%) in the control group.
The median cancer specific survival was 201 months in the screened group and 133 months in the control group.
The risk ratio for death from prostate cancer was 1.16 (95% confidence interval 0.78 to 1.73).
The authors believe that men should be fully informed about the potential hazards of treatment, and the psychological effects of false-positive test results, before they are screened.
They also argue that the next goal for prostate screening should be to find ways of discriminating slow-growing (indolent) tumors from high risk tumors and to develop less aggressive treatment for indolent tumors, rather than to optimize sensitivity of the diagnostic tests.
"After 20 years of follow-up, the rate of death from prostate cancer did not differ significantly between men in the screening group and those in the control group," they conclude. Results from randomized controlled trials of prostate cancer screening have been published in recent years, but none with 20 years of follow-up, they add. Long follow-up is necessary to draw definite conclusions about the benefits of screening.
Randomised prostate cancer screening trial: 20 year follow-up; Sandblom G, Varenhorst E, Rosell J, Löfman O, Carlsson P; BMJ 2011; 342:d1539 doi: 10.1136/bmj.d1539