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Improved survival rate after prostate cancer treatment may reflect a statistical artifact

Many researchers cite improvements in 5- and 10-year survival rates of men treated for prostate cancer as evidence of the effectiveness of prostate-specific antigen (PSA) testing. However, the decline in mortality rate may simply be due to a statistical artifact, suggests a study supported in part by the Agency for Healthcare Research and Quality (HS09578). Since the introduction of PSA testing, the reported incidence of low-grade prostate cancer (which is less likely to spread), measured by the Gleason score, has declined.

However, this appears to be the result of Gleason score reclassification over the past decade, note the researchers.

They used the Connecticut Tumor Registry to examine a group of 1,858 men, aged 75 years and under, who were diagnosed with prostate cancer between 1990 and 1992. They retrieved tissue slides of their prostate tissue, which were reread between 2002 and 2004 by an experienced pathologist blinded to the original Gleason score readings. They then compared prostate cancer mortality rates of the group calculated using the original Gleason score readings with those calculated using the contemporary Gleason score readings.

The contemporary Gleason score readings were significantly higher than the original readings (mean score increased from 5.95 to 6.8), indicating more advanced cancer. As a result, the Gleason score-standardized contemporary prostate cancer mortality rate (1.50 deaths per 100 person-years) appeared to be 28 percent lower than standardized historical rates (2.08 deaths per 100 person-years), even though the overall outcome was unchanged.

See "Prostate cancer and the Will Rogers phenomenon," by Peter C. Albertsen, M.D., James A. Hanley, Ph.D., George H. Barrows, M.D., and others, in the September 7, 2005, Journal of the National Cancer Institute 97(17), pp. 1248-1253.

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