ABSTRACT
Objective: The Modified Gleason Grading System was proposed by the 2005 International Society of Urological Pathology (ISUP) Consensus Conference. In Thailand, prostatic biopsies are mostly diagnosed by general pathologists. The accuracy of the Gleason grading on prostatic biopsies is still questioned. We assessed the accuracy of modified Gleason Grading on prostatic biopsies and detected pitfalls in the grading. Methods: Sixty-nine cases of prostatic biopsies which diagnosed adenocarcinoma were re-examined according to the modified Gleason grading system by an experienced pathologist, four general pathologists and two pathology residents. Results: The accuracy of modified Gleason scores on prostatic biopsies ranged from 79.7% to 98.6% with 68.3 to 100 of 95% CI. Most biopsies with more than one score of difference were missed from Gleason pattern 5. Gleason pattern 5 was found in 25 biopsies. Percents of Gleason pattern 5 were classified into <5% (12 biopsies), 5-10% (6 biopsies), 11-50% (5 biopsies), and >50% (3 biopsies) of the tumor volume. The mean of the number of the observers who fail to detect Gleason pattern 5 in each category was 4 (SD 1.2), 3.6 (SD 1.8), 1.3 (SD 0.95), and 0.33 (SD 0.5), respectively. We found a small amount of Gleason pattern 5 was significantly missed (p = 0.01). Conclusion: The accuracy of Gleason grading on prostate biopsies among general pathologists and pathology residents in this study was fairly good. The missed Gleason pattern 5 is the most common pitfall. Pathologists should be aware of Gleason pattern 5 because it might be present in a prostate biopsy of less than 5 % of the tumor volume.