Frequency and determinants of disagreement and error in gleason scores: a population-based study of prostate cancer.

Background: To examine factors that affect accuracy and reliability of prostate cancer grade we compared Gleason scores documented in pathology reports and those assigned by urologic pathologists in a population-based study.

Methods: A stratified random sample of 318 prostate cancer cases was selected to ensure representation of whites and African-Americans and to include facilities of various types. The slides borrowed from reporting facilities were scanned and the resulting digital images were re-reviewed by two urologic pathologists. If the two urologic pathologists disagreed, a third urologic pathologist was asked to help arrive at a final "gold standard" result. The agreements between reviewers and between the pathology reports and the "gold standard" were examined by calculating kappa statistics. The determinants of discordance in Gleason scores were evaluated using multivariate models with results expressed as odds ratios (OR) and 95% confidence intervals (CI).

Results: The kappa values (95% CI) reflecting agreement between the pathology reports and the "gold standard," were 0.61 (95% CI: 0.54, 0.68) for biopsies, and 0.37 (0.23, 0.51) for prostatectomies. Sixty three percent of discordant biopsies and 72% of discordant prostatectomies showed only minimal differences. Using freestanding laboratories as reference, the likelihood of discordance between pathology reports and expert-assigned biopsy Gleason scores was particularly elevated for small community hospitals (OR = 2.98; 95% CI: 1.73, 5.14).

Conclusions: The level of agreement between pathology reports and expert review depends on the type of diagnosing facility, but may also depend on the level of expertise and specialization of individual pathologists.