Gleason grading: have we gone too far?

Abstract

The Gleason grading system was developed in 1966 as part of a study coordinated by the Veteran's Administration Cooperative Research Group to investigate treatment modalities and prognostic parameters for prostate carcinoma. The grading system underwent several refinements, being finally re-defined in 1974. Since then Gleason grading has been classified as a category 1 prognostic parameter by the College of American Pathologists. It is often stated that this classification is the oldest and most established grading system currently in use. This is contradicted by a variety of modifications that have been proposed over the past 35 years, some of which have been widely adopted into clinical practice. In 2005 the International Society of Urological Pathology Consensus Conference recommended a number of major modifications to the criteria of the Gleason grading classification and these have been embraced internationally. In particular the features defining pattern 3 and pattern 4 tumours have been modified, along with recommendations for deriving a Gleason score for tumours with low volume secondary patterns or with tertiary patterns. These modifications to Gleason grading and scoring have resulted in a significant upgrading of tumours, which itself has the potential to influence decisions regarding the appropriate treatment modality for individual patients. The recommendation that a higher tertiary pattern in needle biopsies should be incorporated into the final Gleason score has been supported in studies correlating final Gleason score with time to biochemical failure, tumour volume and patient outcome. Debate remains regarding the recommendation that the vast majority of tumours with cribriform glands be classified as Gleason pattern 4, as this was not well supported by validating data. Recent publications have taken this further, suggesting that the presence of cribriform glands should no longer be considered a feature of Gleason pattern 3 tumours, although again there is little supporting evidence for this. In view of these current controversies it is recommended that the modified Gleason Scoring Classification should continue to be used in its original (2005) format and that any future alterations should be implemented only when mandated by tumour-related outcome studies.