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Interobserver reproducibility of modified Gleason score in radical prostatectomy specimens
Axel Glaessgen1, Hans Hamberg, Carl-Gustaf Pihl
1Department of Pathology and Cytology, Karolinska Hospital, Stockholm, Sweden.
Abstract:
The Gleason score (GS) of prostate cancer is calculated by adding primary and secondary Gleason grades with patterns occupying less than 5% of the tumour often not included despite their probable prognostic significance. A modified Gleason score (mGS) comprising primary and tertiary patterns of higher grade has been proposed, but its interobserver variability has yet to be elucidated. Slides from 69 consecutive prostatectomy specimens were circulated among four genitourinary pathologists. GS and mGS were assessed, and results were compared in pairs. Mean weighted kappa for GS and mGS were 0.56 (range 0.52-0.66) and 0.58 (range 0.49-0.74), respectively. The difference between GS and mGS was 0, 1 and 2 score units in 66%, 26% and 8%, respectively, mean 0.41 score units (range 0.24-0.51). The increment was greater for transition-zone tumours than for peripheral-zone tumours (0.63 and 0.35 score units, respectively, P=0.002). An odd mGS (5, 7 or 9) was more often given than an odd GS (77% and 62%, respectively, P<0.001). Disagreement between observers greater than 1 score unit was more common with mGS than GS (18% and 4%, respectively, P<0.001). In conclusion, overall mean weighted kappa for interobserver reproducibility of mGS is at least as high as that of GS. However, there is a clustering of mGS in odd scores, and severe disagreement is more commonly observed than with GS. Training of mGS assessment would possibly improve agreement. Tertiary Gleason patterns need to be better defined.
Insights
The modified Gleason score (mGS) shows similar interobserver reproducibility to the standard Gleason score (GS) in prostate cancer grading. However, mGS can lead to more significant disagreements between pathologists, suggesting a need for better training and definition of tertiary patterns.
Area of Science:
- Uropathology
- Oncology
- Prostate Cancer Grading
Background:
- The standard Gleason score (GS) for prostate cancer grading excludes tertiary patterns, potentially missing prognostic information.
- A modified Gleason score (mGS) incorporating tertiary patterns has been proposed, but its reliability among pathologists is unknown.
Purpose of the Study:
- To evaluate the interobserver variability of the modified Gleason score (mGS) compared to the standard Gleason score (GS) in prostate cancer specimens.
Main Methods:
- Four genitourinary pathologists assessed GS and mGS on slides from 69 prostatectomy specimens.
- Interobserver agreement was quantified using weighted kappa statistics and score differences.
- Comparisons were made between GS and mGS, including analysis of score distribution and disagreement levels.
Main Results:
- Mean weighted kappa for mGS (0.58) was comparable to GS (0.56), indicating similar overall reproducibility.
- mGS resulted in a mean score difference of 0.41 units compared to GS, with greater increments in transition-zone tumors.
- More frequent odd scores were assigned with mGS (77%) than GS (62%), and severe disagreement (>1 unit) was higher with mGS (18%) than GS (4%).
Conclusions:
- The modified Gleason score (mGS) demonstrates comparable interobserver reproducibility to the standard Gleason score (GS).
- However, mGS shows a tendency towards odd scores and a higher rate of significant disagreement between pathologists.
- Standardized training for mGS assessment and clearer definitions for tertiary Gleason patterns are recommended to improve diagnostic consistency.