Diagnostic concordance between traditional and digital workflows. A study on 1427 prostate biopsies

OBJECTIVE: To evaluate intra-observer diagnostic reproducibility using traditional slides (TS) versus whole slide images (WSI). METHODS: TS and WSI of 1427 prostatic biopsies (107 consecutive patients) were evaluated by a single pathologist. Agreement between readings was evaluated with Gwet’s Agreement coefficient (AC) and Landis and Koch benchmark scale. RESULTS: The positive/negative agreement between the readings was almost perfect (0.962 AC, 0.949-0.974 95% CI), with method independent distribution of discrepancies. Among positive biopsies, 212 had identical Gleason score (GS) on TS and WSI and discordant GS in 69 cases (AC = 0.932 (0.907-0.956 95% CI). Concordant negative and positive patient classification was observed in 39 and 64 cases, respectively. Two cases were assigned to the positive group on TS and 2 on WSI. Gwet’s AC, was 0.929 (0.860-0.998 95% CI), i.e.: almost perfect agreement. ISUP Grade group (ISUP GG) agreement was evaluated in the 60 concordantly positive cases: in 45 cases it was identical on TS and WSI; in 10 biopsies the discrepancy implied a modification of the assigned ISUP GG of ≤ 1 class and in 5 the discrepancy implied a modification of 2 classes. Gwet’s agreement coefficient was 0.898 (0.834-0.962 95% CI), i. e.: almost perfect agreement. CONCLUSIONS: Our data show almost perfect agreement between digital and traditional diagnostic activity in a routine setting, confirming that digital pathology can be safely introduced into routine workflows.