Atypical intraductal proliferation and intraductal carcinoma of the prostate on core needle biopsy: a comparative clinicopathological and molecular study with a proposal to expand the morphological spectrum of intraductal carcinoma

Aims: Atypical intraductal proliferation (AIP) of the prostate is histologically worse than high-grade prostate intraepithelial neoplasia, but lacks the diagnostic criteria of intraductal carcinoma of the prostate (IDC-P). The aim of this study was to compare the clinicopathological and molecular characteristics (ERG overexpression and PTEN loss) of AIP and IDC-P in core needle biopsies.

Methods and results: One hundred and six [84 (5.6%) of 1480 consecutive and 22 retrospectively collected] cases met the criteria: AIP only (2.4%), IDC-P only (1.3%), and IDC-P coexisting with AIP (2%). Invasive adenocarcinoma [prostate adenocarcinoma (PCa)] was present in 96% and 97% cases of AIP and IDC-P, respectively. The mean number of glands/focus and the largest gland diameter for AIP and IDC-P were 7.6 (range, 2-27) and 11.7 (range, 1-51), and 0.59 mm (range, 0.2-1.1 mm) and 0.75 mm (range, 0.2-1.8 mm), respectively. For AIP, loose cribriform architecture was the most common (93%) morphology. IDC-P-associated PCa had more aggressive pathology, including the highest combined Gleason score (GS), high-grade GS ≥ 4 + 3, and largest percentage involvement of core by PCa and percentage positive cores, than AIP-associated PCa (P < 0.05). Within the AIP group, ERG status and PTEN status were similar to those of adjacent PCa in 97% and 88% of cases, respectively. Within the IDC-P group, ERG status and PTEN status were similar among IDC-P, AIP and PCa in 96% and 91% of cases, respectively. PTEN loss was frequently heterogeneous in PCa, and localized adjacent to AIP or IDC-P.

Conclusions: AIP represents a lower-grade morphological spectrum of IDC-P, associated with intermediate-risk PCa. Patients with only AIP need an immediate repeat biopsy to rule out clinically significant PCa.