Amanda H. Seipel, Brett Delahunt, Hemamali Samaratunga, Lars Egevad

Ductal adenocarcinoma of the prostate (DAC) is recognised as a subtype of prostatic adenocarcinoma, but its diagnostic criteria and biology remain controversial. DAC was first thought to stem from Müllerian duct remnants, but further studies suggest a prostatic origin. DAC is composed of tall, columnar, pseudostratified epithelium with a papillary, cribriform, glandular or solid architecture. The diagnosis is based on morphology alone with papillary architecture being the most helpful diagnostic feature. The tumour is rare in a pure form and most cases are combined with acinar adenocarcinoma. The most common differential diagnoses of DAC are intraductal carcinoma of the prostate and high-grade prostatic intraepithelial neoplasia. Patients often present at an advanced clinicopathological stage. High rates of extra-prostatic extension, seminal vesicle invasion, local and regional metastases, and positive surgical margins are seen after radical prostatectomy. DAC metastasises to sites that are less commonly seen for prostate cancer such as lung, brain, testis and penis. The morphology and the unusual metastatic locations make the accurate diagnosis of metastases challenging, but a positive immunostain for prostate specific markers may be helpful. The correct identification of DAC has implications for treatment as well as outcome.