Classification of prostatic adenocarcinoma as favourable/unfavourable histology has high interobserver agreement in prostate needle core biopsies

Aims A dichotomous classifier for prostatic adenocarcinoma, favourable and unfavourable histology, was recently proposed to optimize metastasis prediction. We evaluate interobserver agreement for its classification. Methods and results Fifty biopsies with prostatic adenocarcinoma were selected. One slide per biopsy was scanned using the Aperio AT2 scanner (20x) and viewed in Leica Web Viewer. Ten pathologists reviewed each slide after completing a training module. Biopsies were scored for Grade Group (1–5) and presence of unfavourable histology. Forty‐one of 50 biopsies (82%) had unanimous consensus [13 (32%) unfavourable and 28 (68%) favourable], 47 (94%) for at least 9 of 10 reviewers, and 48 (96%) for at least 8 of 10 reviewers. Percent agreement for favourable/unfavourable classification was 94%, kappa = 0.88 (95% CI: 0.8, 0.96), and Gwet's AC1 coefficient = 0.90 (95% CI: 0.82, 0.97) [both P ‐value < 0.001]. Inter‐rater agreement for Grade Group designation was evaluated in biopsies with 100% consensus. In the favourable consensus group ( n = 28), kappa for Grade Group was 0.80 (95% CI: 0.62, 0.98) and Kendall's W was 0.83 (95% CI: 0.81, 0.89), with both P ‐value < 0.001. For the unfavourable consensus group ( n = 13), kappa for Grade Group was 0.56 (95% CI: 0.36, 0.75) and Kendall's W was 0.78 (95% CI: 0.76, 0.85), with both P ‐value < 0.001. Conclusions The classification of prostatic adenocarcinoma as favourable/unfavourable histology has high interobserver agreement, even when learnt through a simple tutorial. GG designation was more variable. This provides evidence that the favourable/unfavourable classification could be utilized in routine practice given its ease of use.