Gleason scoring varies among pathologists and this affects clinical risk in patients with prostate cancer

To investigate whether our practice of specialist review of all diagnostic biopsies was necessary to prevent misgrading of referred prostate cancer patients, and whether this misclassification, if any, would have resulted in misclassification of clinical risk grouping (Seattle Risk Grouping [SRG]) and subsequent treatment strategy and prognosis.

Important prognostic indicators for prostate cancer include the presenting prostate-specific antigen (PSA), clinical stage and Gleason sum of the tumour. These three variables are incorporated into the SRG cohorts to establish treatment strategy. Patients with prostate cancer referred for brachytherapy had their prostate biopsies reviewed by a reference pathologist (PD) with a special interest in prostate cancer. We compared the agreement between the scoring of the referring pathologists with that of PD, and evaluated if any differences changed the SRG and therefore the clinical risk and treatment strategy for the patients.

In only 52% (43/83) of cases, was there total agreement between the two sets of pathologists. The inter-rater agreement was statistically 'fair' (unweighted kappa statistic 0.27). In 90% (36/40) of cases with disagreement, PD assigned higher Gleason sums. In 40% (16/40) of cases with disagreement, the change in Gleason sum altered the SRG; in one out of 16 cases, the SRG was downgraded from 'intermediate' to 'low' risk disease; in six out of 16 cases, it was upgraded from 'low' to 'intermediate' risk, and, in nine out of 16, from 'intermediate' to 'high' risk.

Our findings confirm previous reports of only limited correlation between pathologists in reporting Gleason sums. In this study, 19% (16/83) of cases had their grading changed to a level that altered clinical risk, almost always (94%; 15/16) to one that worsened prognosis. This would have significantly affected treatment strategy for these patients, and thus we recommend that all centres ensure accurate Gleason grading by the use of pathologists with special interests in prostate cancer.