Interobserver variability in Gleason histological grading of prostate cancer.

OBJECTIVE The aims of this study were to evaluate the reproducibility of the Gleason grading system and to compare its interobserver variability with the novel Gleason grade grouping proposal using a large sample volume. MATERIALS AND METHODS In total, 407 pathology slides of prostate needle biopsies from 34 consecutive patients with prostate cancer were re-evaluated. The International Society of Urological Pathology 2005 modified Gleason grading system with Epstein's modification was used. Two pathologists, blind to each other and to the initial pathology report, performed the pathological evaluation. To determine interobserver concordance, the kappa (κ) coefficient test was used. RESULTS Pathologist 1 and pathologist 2 detected a tumor in 202 and 231 cores, respectively (p < 0.001). The two pathologists disagreed on the presence of a tumor in 31 cores. Of these 31 cores, 74% (n = 23/31) were Gleason pattern 3. The mean length of the cancer foci in these 31 disputed cores was 1.54 ± 0.8 mm. Concordance rates between the two observers for primary and secondary Gleason patterns were 63.96% (κ = 0.34) and 63.45% (κ = 0.37), respectively. Concordance with respect to the Gleason sum was 57.9% (κ = 0.43). When the Gleason scores were classified into the novel Gleason grade grouping, concordance was found to be 51.7% (κ = 0.39). CONCLUSIONS The agreement between observers on the Gleason sum was moderate. The novel Gleason grade grouping did not improve interobserver agreement. Further studies are needed to confirm these results on interobserver variability.