Duct Quest: An international survey of genitourinary and community pathologists reveals diagnostic uncertainties in separating atypical intraductal proliferation from high-grade prostatic intraepithelial neoplasia and intraductal carcinoma of the prostate.

Atypical intraductal proliferations of the prostate encompass a spectrum from high-grade prostatic intraepithelial neoplasia (HGPIN) to intraductal carcinoma of the prostate (IDCP), the latter being strongly associated with aggressive prostate cancer. The recent WHO classification introduced atypical intraductal proliferation (AIP) to describe lesions intermediate between HGPIN and IDCP. To assess current diagnostic practice and variability prior to implementation of new consensus recommendations, we surveyed 541 pathologists from four national and international pathology societies (Genitourinary Society of Pathology (GUPS), International Society of Urological Pathology (ISUP), British Association of Urological Pathology (BAUP), and German Division of the International Academy of Pathology (GDIAP)). Participants widely supported the Guo/Epstein criteria for diagnosing IDCP and generally agreed that when IDCP is found in the absence of high-grade cancer on needle biopsy, unsampled high-grade cancer is almost always present, reinforcing its role as an exclusion criterion for active surveillance. However, opinions varied on whether IDCP is a precursor lesion or a growth pattern of invasive cancer. Participants reviewed 25 images of intraductal lesions classified as benign, HGPIN, AIP, or IDCP. Consensus (>2/3 agreement) was reached in only 36% of cases, and no AIP case achieved consensus. Grouping lesions into low-grade (benign/HGPIN) versus high-grade (AIP/IDCP) categories increased consensus to 88%. Consensus was higher for AIP + IDCP (60%) than for HGPIN + AIP (32%), suggesting closer diagnostic alignment of AIP with IDCP. These findings highlight persistent interobserver variability and the need for clearer diagnostic criteria, education, and further biological characterization of AIP and IDCP.