CONTEXT: Prostatic adenocarcinoma growing within acinar-ductal spaces (intraductal carcinoma) in contrast to high-grade prostatic intraepithelial neoplasia (HG-PIN) impacts negatively on patient outcome. There is currently no generally accepted definition of this lesion nor is it classified in the current prostate cancer grading system (Gleason).

OBJECTIVE: To define intraductal carcinoma of the prostate (IDC-P) with major and minor diagnostic criteria that clearly separate it from HG-PIN. The implications of such a lesion are discussed with proposals to incorporate this entity into the Gleason grading system.

DATA SOURCES: We reviewed all published data referring to intraductal spread of prostate carcinoma. Articles discussing endometrial, endometrioid, and ductal carcinoma are included.

CONCLUSIONS: Intraductal carcinoma of the prostate as defined by major criteria that include enlarged gland structures, neoplastic cells spanning the gland lumen, central comedonecrosis, and further supported by minor diagnostic criteria including molecular biological markers, separate this entity from HG-PIN. Despite its perimeter basal cells, IDC-P should be interpreted as biologically equivalent to Gleason pattern 4 or 5 adenocarcinoma. Several hypotheses are proposed as to the evolution of IDC-P, which is almost always a late event in prostate carcinoma progression. Diagnosis of IDC-P on needle biopsy should prompt therapeutic intervention rather than surveillance or repeat biopsy, as is the case for HG-PIN.