Decade-long Gleason shift may influence study conclusions

May 23, 2005

Prostate cancer studies that compare contemporary outcomes with historic controls should be viewed with the understanding that Gleason scores quietly have been climbing for the past 10 years. This observation is more than a curiosity because clinicians and others use Gleason scores to stage cancers and establish prognoses, and epidemiologists apply them to end results when trying to determine the effect that procedures and therapies have on outcomes.

Prostate cancer studies that compare contemporary outcomes with historic controls should be viewed with the understanding that Gleason scores quietly have been climbing for the past 10 years. This observation is more than a curiosity because clinicians and others use Gleason scores to stage cancers and establish prognoses, and epidemiologists apply them to end results when trying to determine the effect that procedures and therapies have on outcomes.

"Our language has changed," Peter C. Albertsen, MD, MS, professor and chief of the division of urology at the University of Connecticut Health Center, told Urology Times. "Anyone who wants to use historical controls should have the old slides re-read because the yardstick has changed. It is like inflation. A dollar today is not the same as the dollar of 10 years ago."

The phenomenon Dr. Albertsen described in the study he presented here yesterday is called "Gleason shift" and was first documented in lung cancer studies. He decided if a Gleason shift might be making itself felt in prostate cancer studies when he noted recent studies suggesting that the incidence of low-grade cancer had declined since the early 1990s.

Histology slides from a population-based cohort of 1,858 men aged 70 years or younger who were diagnosed with prostate cancer between 1990 and 1992 were collected and read by three pathologists who were blinded to the original readings. The slides were read by three pathologists who were blinded to the initial findings. In the contemporary readings, all Gleason 2 and 3 scores disappeared while the percentage of slides interpreted as Gleason 6 rose from around 24% in 1990-'92 to close to 44% in the contemporary interpretation of the slides. Owing to the size of the cohort, the study's evidence of Gleason upgrading readily achieved statistical significance (p=.001).

Dr. Albertsen was not quite ready to identify specific reasons for the shift but he did note that, "the phenomenon coincides with the introduction of the spring-loaded biopsy gun. We are not seeing big transurethral resection specimens anymore. Almost all diagnoses are made from a much smaller specimen.

"The take-home message is that we have seen a shift in Gleason scores over the last decade and it will impact anyone who does comparisons of historical series with contemporary series," Dr. Albertsen said.