(HealthDay News) — Since the introduction of prostate-specific antigen (PSA) screening there has been a large reduction in advanced-stage cancers but only a modest drop in cancers with a high Gleason score, suggesting that patients with lower-grade disease do not progress to higher grade over time and may benefit from active surveillance, according to a study published in the Aug. 15 issue of Cancer Research.

Kathryn L. Penney, Sc.D., from Brigham and Women’s Hospital in Boston, and colleagues compared the distribution of grade and clinical stage over time among 1,207 health professionals who were diagnosed with prostate cancer from 1982 to 2004, representing the pre-PSA and post-PSA screening eras, and treated with prostatectomy.

The researchers found that the percentage of advanced-stage cancers fell more than six-fold, from 19.9% (stage T3 or greater) from 1982 to 1993 to 3% (all stage T3) from 2000 to 2004. However, the percentage with a Gleason score of 8 or more fell only 30% over these periods, from 25.3% to 17.6%. There was a significant association noted between grade and stage by time period.

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“As the dramatic shift in stage since the introduction of PSA screening was accompanied by a more modest shift in Gleason grade, these findings suggest that grade may be established early in tumor pathogenesis,” Penney and colleagues conclude. “This has implications for the understanding of tumor progression and prognosis, and may help patients diagnosed with lower-grade disease feel more comfortable choosing active surveillance.”