According to the results of a study published in the Journal of the National Cancer Institute, the frequency of interval prostate cancers-cancers diagnosed on the basis of symptoms in between scheduled screening tests-was similar regardless of whether PSA testing occurred every two years or every four years.
Men 50 years of age or older in the U.S. are often offered prostate-specific antigen (PSA) testing for the early detection of prostate cancer. The PSA test measures proteins that are produced and shed by the prostate. PSA levels tend to be elevated when prostate cancer is present, but levels can also be elevated in benign (non-cancerous) conditions affecting the prostate.
Although PSA screening may allow for the earlier detection and treatment of prostate cancer, there is little evidence thus far that it reduces the risk of dying of prostate cancer. Furthermore, PSA screening can carry risks. Some prostate cancers identified by PSA screening may be slow growing and unlikely to cause health problems during the man’s lifetime; men treated for these cancers will experience the adverse effects of cancer treatment without gaining a health benefit. Furthermore, as with any screening test, there is a possibility of a false-positive test. Men with a false-positive test may to undergo an unnecessary prostate biopsy.
A factor that will influence the performance of PSA testing is the interval between screening tests. While annual screening is common in the U.S., a large clinical trial in Europe utilized less frequent screening. Study participants in Gothenburg, Sweden, were screened every two years and study participants in Rotterdam, The Netherlands, were screened every four years. One potential concern with the longer screening interval is that it could increase the number or severity of interval cancers. Interval cancers are cancers diagnosed on the basis of symptoms in between scheduled screening tests.
The frequency and characteristics of interval cancers were compared among men in Gothenberg and Rotterdam. An interval cancer was classified as aggressive if it had one of the following characteristics: 1) had spread to lymph nodes or distant sites in the body; 2) was linked with a PSA concentration of greater than 20.0 ng/mL; or 3) had a Gleason score greater than 7.
- Overall, during a ten-year period, prostate cancer was diagnosed in 8.4% of men screened every four years and 13.1% of men screened every two years.
- Interval cancers were no more common among men screened every four years than among men screened every two years. Interval cancers were diagnosed in 0.43% of men screened every four years and 0.74% of men screened every two years.
- The frequency of aggressive interval cancers was also similar in the two study groups.
The researchers conclude that although more prostate cancers were diagnosed overall among men screened every two years than among men screened every four years, the frequency of interval cancers was low in both groups. The longer screening interval (four years rather than two years) did not increase the frequency of interval cancers.
Some concerns about this study were discussed in an accompanying editorial. Because decisions about PSA testing can be complicated, men are encouraged to discuss the risks and benefits with their physician.
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 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. Journal of the National Cancer Institute. 2007;99:1296-303.
 Crawford ED. Is a screening interval of every 4 years for prostate cancer acceptable? Journal of the National Cancer Institute. 2007;99:1279-1280.
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