Interobserver and intraobserver reproducibility in digital and routine microscopic assessment of prostate needle biopsies

Advances in whole slide digital imaging in the past decade necessitate validation of these tools in each organ system in advance of clinical adoption. We assessed reproducibility in reporting prostate needle biopsy parameters among urologic pathologists using routine and digital microscopy in a consultation/second opinion-like setting. Four urologic pathologists evaluated a single core level from 50 diagnostically challenging needle biopsy specimens by routine microscopy and whole slide digital imaging. Interobserver and intraobserver agreement were calculated for primary and secondary Gleason grades, Gleason score, tumor quantitation (percentage and size in millimeters), and perineural invasion. Interobserver agreement for routine microscopy was excellent for primary Gleason grade (κ = 0.72) and good for all other parameters (κ ranging from 0.36 to 0.55). Whole slide digital imaging assessment yielded similar agreement for all parameters. Intraobserver agreement for primary Gleason grade and Gleason score was very good to excellent for all pathologists (all κ ≥ 0.65 and ≥ 0.73, respectively). Size of tumor in millimeters consistently displayed higher levels of agreement than percentage of tumor across media and pathologists. Digital assessment of routinely reported cancer parameters on prostatic needle biopsy for a given scanned core level is comparable to that of routine microscopy. These findings imply that histologic interpretation using dynamic whole slide images may accurately simulate routine microscopic evaluation in the consultation setting. Implementation of whole slide digital imaging in these scenarios may significantly reduce the workload of large referral centers in the near future and impact the manner in which pathologists seek second opinion consultation on challenging cases.