Intraductal Carcinoma of the Prostate (IDC-P) and Atypical Intraductal Proliferation (AIP)

Abstract

Intraductal carcinoma of the prostate (IDC-P) is an intraglandular/ductal neoplastic proliferation of prostatic glandular epithelial cells that is characterized by marked expansion of glandular architecture and nuclear atypia that often exceeds than seen in invasive carcinoma. It has been long recognized that some “invasive” prostatic carcinomas had residual basal cells on H&E staining or basal cell immunostains. McNeal and Yemoto first reported that it represented an aggressive form of acinar carcinoma. The concept of IDC-P has evolved significantly since then to culminate in recognizing it as a distinct entity in the 2016 WHO blue book.

Two morphological hallmarks of IDC-P are expansile growth of atypical cells that forms large dense cribriform and/or solid architecture and intraductal/acinar location of the atypical cells with preservation of basal cells. IDC-P is a clinically aggressive form of prostate cancer that is typically associated with a high Gleason score, large tumor volume, extraprostatic extension, positive lymph node status, and increased recurrence risk. A diagnosis of IDC-P in biopsy mandates immediate repeat biopsy or definitive therapy even in the absence of documented invasive PCa. Therefore, an accurate recognition of IDC-P and its distinction from HGPIN are crucial to patient management. A lesion that histologically appears more ominous than HGPIN but do not fulfill the criteria of classical IDC-P is termed as atypical intraductal proliferation (AIP). AIP is typically characterized by loose cribriform proliferations lacking intraluminal necrosis and nuclear atypia that is characteristic of IDC-P. Such lesions in the past have also been referred to as atypical cribriform lesion (ACL) or atypical intraductal cribriform proliferation. Emerging molecular studies have shown distinct differences between IDC-P and HGPIN but similarity between IDC-P and AIP. This chapter summarizes the current concepts on morphologic and molecular characteristics of IDC-P, its differential diagnoses, and an approach to work-up of atypical intraductal proliferative lesions in prostate needle biopsies.