According to a study published in the Journal of the National Cancer Institute, prostate cancers today receive a higher Gleason score than the same cancers would have a decade ago; this shift in grade may explain some of the apparent improvement in prostate cancer survival.
The prostate is a gland of the male reproductive system, which produces some of the fluid that transports sperm during ejaculation. After skin cancer, prostate cancer is the most common form of cancer diagnosed in men. Current treatment options include watchful waiting (delay of treatment until signs of cancer progression), surgery, chemotherapy, radiation, and/or hormonal therapy. Cancer that is removed by surgery or biopsy will be classified according to the Gleason Grading System for prostate cancer. This grading system, on a scale of 2-10, helps physicians predict how rapidly the cancer is likely to spread. Higher Gleason scores are associated with more advanced and more rapidly growing cancers than lower scores.
Over the past several years, the average Gleason score assigned to prostate cancers had increased. The may be due to either an increase in the number of aggressive cancers being identified, or it may reflect changes in how pathologists assign Gleason scores.
In order to evaluate which of these scenarios is more likely, researchers evaluated biopsy specimens from 1858 prostate cancer patients diagnosed between 1990 and 1992. The biopsy specimens were re-reviewed by a pathologist who was not aware of the original Gleason score; the original and more recent Gleason scores were compared. The more recently assigned score was significantly higher than the original score. At the time of diagnosis in 1990-1992, the average Gleason score assigned to these cancers was 5.95; when the specimens were re-reviewed for this study, the same cancers received an average score of 6.8. Because of this shift in scoring, Gleason-adjusted survival was better using the more recent Gleason scores than using the original scores, even though none of the patient outcomes had changed. For example, patients currently given a high Gleason score will have, on average, less aggressive cancer and better survival than patients given a high Gleason score a decade ago. This change is caused simply by how pathologists apply the scoring system.
The researchers conclude that the increase in Gleason scores in recent years is explained at least in part by changes in use of the Gleason system, rather than by changes in the types of prostate cancers being diagnosed. Some of the grade-specific improvements in prostate cancer survival in recent years may be the result of this Gleason score shift.
Reference: Albertson PC, Hanley JA, Barrows GH et al. Prostate Cancer and the Will Rogers Phenomenon. Journal of the National Cancer Institute. 2005;97:1248-53.
Accompanying editorial: Thompson IM, Canby-Hagino E, Lucia MS. Stage migration and grade inflation in prostate cancer: Will Rogers meets Garrison Keillor. Journal of the National Cancer Institute.2005;97:1236-1237.