More prostate cancers were detected among men who were screened every two years than men screened every four years, according to a study published online August 28 in the Journal of the National Cancer Institute. But the shorter time between screenings did not reduce the number of aggressive cancers found between the scheduled screening tests.
Since the introduction of PSA (prostate specific antigen) testing in the late 1980s, the incidence of prostate cancer has risen dramatically. The rise is mainly due to widespread screening of asymptomatic men. Screening for prostate cancer is a controversial issue because evidence is lacking that PSA screening prevents prostate cancer deaths. Looking at the rate of interval cancers--cancers diagnosed based on symptoms during the years between screening tests--may give an indication of how well a screening program is working.
Monique Roobol, Ph.D., of Erasmus Medical Centre in Rotterdam, The Netherlands, and colleagues conducted a study to determine whether the time between PSA screenings influenced the incidence of prostate cancer. They analyzed data collected at two European medical centers that participated in the European Randomized Study of Screening for Prostate Cancer.
At a center in Gothenburg, Sweden, 4,202 men were screened every two years, and in Rotterdam, The Netherlands, 13,301 men were screened every four years. The researchers compared both the number and characteristics of the interval prostate cancers diagnosed in these men. Serious, potentially life threatening interval cancers were analyzed separately.
Over a period of ten years, the overall incidence of prostate cancer was higher among men screened every two years than among those screened every four years (13.14 percent vs. 8.41 percent). But the total number of interval cancers that were diagnosed between screening tests was 31 (0.74 percent) in Gothenburg and 57 (0.43 percent) in Rotterdam. This difference in the number of interval cancers and the number of aggressive interval cancers at the two centers was not statistically significant, indicating that the two-year screening program did not reduce the number of interval cancers as would be expected.
"It is therefore more realistic to believe that each screening will again lead to prostate cancer diagnoses among some men from a large pool harboring small and often clinically insignificant disease and thus that more cancers were detected in Sweden because screening was more frequent," the authors write. Additionally, larger cancers seem to be identified with equal effectiveness if screening takes place every 2 or 4 years.
In an accompanying editorial, E. David Crawford, M.D., of the University of Colorado Health Sciences Center in Aurora discusses the controversy surrounding prostate cancer screening and the challenge in determining how often to screen.
"Although many of us believe that early detection is saving lives, definitive evidence is lacking," Crawford writes.
Article: Roobol MJ, Grenabo A, Schröder FH, Hugosson J. Interval Cancers in Prostate Cancer Screening: Comparing 2- and 4-Year Screening Intervals in the European Randomized Study of Screening for Prostate Cancer, Gothenburg and Rotterdam. J Natl Cancer Inst 2007; 99:1296-1303
Editorial: Crawford ED. Is a Screening Interval of Every 4 Years for Prostate Cancer Acceptable" J Natl Cancer Inst 2007; 99: 1279-1280
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