Microscopic description and IHC:
The prostate biopsy shows fused glands with an infiltrative pattern. The nuclei are enlarged, hyperchromatic and have prominent nucleoli. P63 and CK5 staining is negative indicating loss of basal cells. AMACR is strongly positive.
Discussion:
Fused glandular architecture, enlarged nuclei, prominent nucleoli, infiltrative appearance, loss of basal cells, and AMACR positivity are all features of prostate adenocarcinoma, particularly Gleason pattern 4. The prostate biopsy consists of back to back fused glands without other secondary patterns. The prostate triple staining pattern essentially eliminates all other answer choices as well.
Other helpful diagnostic features of prostatic adenocarcinoma (not present in this case) include blue mucin, pink crystalloids, sharp luminal borders, and perineural invasion.