Rare histological patterns of prostatic ductal adenocarcinoma

Aims: 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. Methods: 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. Results: 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. Conclusions: 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.