Trends in Gleason score for prostate cancer diagnosed between 1983 and 1993

Purpose: During the 1980s and 1990s the number, incidence rate and proportion of moderately differentiated prostate cancer cases ascertained by population based cancer registries increased substantially. The increase is thought to have resulted from the widespread use of prostate specific antigen (PSA) for screening because it occurred coincidentally with the introduction of PSA for early detection of prostate cancer. We investigate this increase in a population based study. Materials and Methods: To report the trends in tumor grade we conducted a blinded, standardized pathological study and reviewed medial records of a stratified random sample of cases diagnosed before and after the introduction of PSA (1983 to 1984 and 1992 to 1993). Archival tumor biopsy specimens or transurethral resection of the prostate specimens were reviewed for the diagnosis of cancer and assignment of Gleason score. Medical records were reviewed to determine the method of prostate cancer detection for each case. Results: We found a small but statistically insignificant shift in the distribution of Gleason scores assigned after review of biopsy or transurethral resection specimens. The proportion of Gleason score 2, 3 and 4 tumors decreased, and the proportion of 7, 8, 9 and 10 tumors as a group did not change. The shifts in Gleason score resulted in a slight statistically nonsignificant increase in mean Gleason score. There was a significant shift in the method of detection from predominately incidental detection in the earlier period to predominately screen detection in the later period. Because the proportion of screen detected tumors increased and they had a significantly higher mean Gleason scare than incidentally detected tumors within each interval, the overall mean Gleason score increased. Conclusions: After a standardized pathological review a small shift in the distribution of Gleason scores occurred resulting in a small increase in mean Gleason score between 1983 and 1984, and 1992 and 1993. There was little change in the proportion of Gleason score 7, 8, 9 and 10 tumors between the 2 periods.