Answer: D - Prostatic ductal adenocarcinoma

Microscopy reveals small papillary fronds lined by columnar cells showing pseudostratification with mild nuclear atypia and prominent nculeoli. The linings shows diffuse expression of Nkx3.1 and AMACR, and scattered basal cells are identified (patchy expression of p63 and high molecular weight cytokeratin). The features are diagnostic of prostate ductal adenocarcinoma (PDA). 

PDA is a rare form of prostate carcinoma. It was initially reported as “endometrioid carcinoma of prostatic utricle” in peri-uretheral prostate, resulting in obstructive symptoms. Nowadays we identify PDA in any prostate zone. The diagnostic feature is papillary structures (with or without large dilated complex glands) lined by tall columnar cells, commonly showing pseudostratification of nuclei. Based on the architectural pattern, it is graded as Gleason pattern 3, 4 or 5. The current tumor is compatible with Gleason 4+4=8 (grade group 4). Presence of scattered basal cells does not confer the diagnosis of PDA.

It is of note that PSA is not a useful screening method for PDA as elevation is less common than conventional acinar prostate adenocarcinoma (PSA of current case at the time of diagnosis was 1.0 ng/ml).