Utility of Pathology Imagebase for Standardization of Prostate Cancer Grading

Abstract

Aims

Despite efforts to standardize grading of prostate cancer, there is still a considerable variation in grading practices even among experts. In this study we describe the use of Pathology Imagebase, a novel reference image library, for setting an international standard in prostate cancer grading.

Methods and Results

The International Society of Urological Pathology (ISUP) recently launched a reference image database supervised by experts. A panel of 24 international experts in prostate pathology independently reviewed microphotographs of 90 cases of prostate needle biopsies with cancer. A linear weighted kappa of 0.67 (95% confidence interval 0.62 - 0.72) and consensus was reached in 50 cases. The inter-observer weighted kappa varied from 0.48 to 0.89. The highest level of agreement was seen for Gleason score (GS) 3+3=6 (ISUP grade 1), while higher grades and particularly GS 4+3=7 (ISUP grade 3) showed considerable disagreement. Once a 2/3 majority was reached, images were automatically moved into a public database available for all ISUP members at www.isupweb.org. Non-members are able to access a limited number of cases.

Conclusions

It is anticipated that the database will assist pathologists to calibrate their grading and, hence, decrease inter-observer variability. It will also help identify instances where definitions of grades need to be clarified.

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