A UK-based investigation of inter- and intra-observer reproducibility of Gleason grading of prostatic biopsies.
AIMS: The frequency of prostatic core biopsies to detect cancer has been increasing with more widespread prostate specific antigen (PSA) testing. Gleason score has important implications for patient management but morphological reproducibility data for British practice are limited. Using literature-based criteria nine uropathologists took part in a reproducibility study. METHODS: Each of the nine participants submitted slides from consecutive cases of biopsy-diagnosed cancer assigned to the Gleason score groups 2-4, 5-6, 7 and 8-10 in the original report. A random selection of slides was taken within each group and examined by all pathologists, who were blind to the original score. Over six circulations, new slides were mixed with previously read slides, resulting in a total of 47 of 81 slides being read more than once. RESULTS: For the first readings of the 81 slides, the agreement with the consensus score was 78% and overall interobserver agreement was kappa 0.54 for Gleason score groups 2-4, 5-6, 7, 8-10. Kappa values for each category were 0.33, 0.56, 0.44 and 0.68, respectively. For the 47 slides read more than once, intra-observer agreement was 77%, kappa 0.66. The study identified problems in core biopsy interpretation of Gleason score at levels 2-4 and 7. Patterns illustrated by Gleason as 2 tended to be categorized as 3 because of the variable acinar size and unassessable lesional margin. In slides with consensus Gleason score 7, 13% of readings were scored 6 and in slides with consensus 6, 18% of readings were scored 7. CONCLUSIONS: Recommendations include the need to increase objectivity of the Gleason criteria but limits of descriptive morphology may have to be accepted.