Diagnosis and Reporting of Intraductal Carcinoma of the Prostate: A Guide for Practising Pathologists With Excerpts From the Genitourinary Pathology Society and the International Society of Urological Pathology Joint Expert Consultation.

Atypical intraductal proliferations of the prostate span a spectrum from high-grade prostatic intraepithelial neoplasm (HGPIN) to intraductal carcinoma of the prostate (IDCP), with progressively more atypical architectural and cytologic features and at least partial retention of basal cells. IDCP is strongly associated with coexisting high-grade, advanced invasive prostate cancer (PCa). In contrast, unifocal HGPIN is not associated with a significantly increased risk of PCa on subsequent biopsies. Atypical intraductal proliferation (AIP), the term recommended by WHO for proliferations with morphologic features borderline between HGPIN and IDCP, shares molecular and clinicopathological traits with IDCP and serves as a marker of unsampled adverse pathology. Despite progress in understanding IDCP and AIP, their accurate diagnosis and reporting remain challenging. This review provides recommendations on the diagnosis and reporting of IDCP and AIP, stemming from a recent joint expert consultation of the Genitourinary Pathology Society and the International Society of Urological Pathology, to help surgical pathologists optimally diagnose and report atypical intraductal proliferations. The diagnosis of IDCP in biopsies and resections should follow the updated Guo and Epstein criteria, with basal cell immunohistochemistry as needed. Rarely, marked (pleomorphic/bizarre) intraductal cytologic atypia alone may suffice for an IDCP diagnosis. The term AIP should be used only when proliferations are equivocal yet favor IDCP; such cases should be reported as "AIP, suspicious for IDCP." The diagnosis of cribriform HGPIN should not be made on biopsy; instead, such atypical lumen-spanning proliferations with loose cribriform architecture should be reported as "AIP, suspicious for IDCP." When available, ERG and PTEN immunohistochemistry can help differentiate from HGPIN. Adopting these recommendations would reduce interobserver variability, promote consistent communication with clinicians, and enhance patient management.