Rare histological patterns of prostatic ductal adenocarcinoma

Prostatic ductal adenocarcinomas account for 1% of prostate cancers. Most commonly, these lesions grow in large cribriform and/or papillary patterns or, as recently described, in a manner resembling prostatic intraepithelial neoplasia (i.e., 'PIN-like' prostatic ductal adenocarcinoma). This study aims to report rare variants of ductal adenocarcinoma.

Ten cases of rare patterns of prostatic ductal adenocarcinoma that have not been formally investigated prior to this study, primarily from one author's consultation service (1987-2009), were selected.

Two (n = 2) cases were prostatic ductal adenocarcinoma with mucinous and goblet cell features. Three (n = 3) cases are the first described cases of foamy gland prostatic ductal adenocarcinoma. Other unique cases were prostatic duct adenocarcinomas with associated Paneth cell-like neuroendocrine (n = 2), micropapillary (n = 2), and cystic papillary features (n = 1). Prostatic origin was confirmed with immunohistochemical studies for prostate specific antigen (PSA), P501S, and prostate specific membrane antigen (PSMA). High-grade PIN was ruled out with negative stains for high molecular weight cytokeratin (HMWCK) and p63. Four prostatic ductal adenocarcinomas had no evidence of disease at 2-8 years follow-up: foamy gland, Paneth cell-like, and micropapillary (two cases). One mucinous prostatic ductal adenocarcinoma resulted in the patient's death and the other mucinous case was alive at 7 years and 2 months, yet with no information as to status of disease. The remaining four cases were lost to follow-up, died of other causes, or were recent.

In summary, we report several rare and unique histological patterns of prostatic ductal adenocarcinoma. The practical importance of recognising these histological variations is that in some cases they may be misdiagnosed as non-prostatic tumours. These unusual cases also provide further support for the relationship between acinar and ductal adenocarcinoma.