Answer: Non-specific granulomatous prostatitis and adenocarcinoma of the prostate

Histology: Several of the prostate glands are surrounded by a collection of histiocytes, lymphocytes, plasma cells and numerous eosinophils. In addition, there is a crowded proliferation of small glands which are similarly inflamed. These glands have small but visible nucleoli. A triple cocktail stain for basal cell markers (p63 and high molecular weight cytokeratin) and AMACR (racemase) shows the small glands to lack basal cells and are positive in their cytoplasm for racemase.

Discussion: These needle biopsies show the typical features of non-specific granulomatous prostatitis consisting of a polymorphous inflammatory infiltrate composed of lymphocytes, plasma cells, neutrophils and eosinophils. The amount of eosinophils can vary in non-specific granulomatous prostatitis and when very prominent as seen in this case may be confused with allergic prostatitis. Allergic prostatitis is exceedingly rare and should not be diagnosed in the absence of severe systemic allergic symptoms such as asthma and peripheral eosinophilia. Furthermore, allergic prostatitis is characterized by sheets of eosinophils typically without the accompanying other inflammatory cells. In addition to the non-specific granulomatous prostatitis seen in this case, there is a focal collection of crowded small glands architecturally suspicious for adenocarcinoma. One must be extremely cautious in diagnosing adenocarcinoma in the setting of an inflamed prostate as inflammation can result in both architectural and cytological features mimicking carcinoma. However, in this case the immunohistochemical stain is very helpful in establishing a malignant diagnosis in that all of the small glands entirely lack basal cells and are positive for racemase. The triple cocktail stain also highlights the infiltrative nature of the small glands around pre-existing benign glands which are uniformly labeled with basal cell markers. It is likely in this case that the adenocarcinoma is an incidental finding and what caused the elevated serum PSA levels was the non-specific granulomatous prostatitis. Non-specific granulomatous prostatitis can clinically closely mimic adenocarcinoma of the prostate with elevated PSA levels up to 30 ng/ml, a rock hard irregular prostate characteristic of prostate cancer and ultrasound findings typical of prostate cancer. Although most cases of non-specific granulomatous prostatitis as in the current case do not histologically resemble adenocarcinoma of the prostate, there is an epithelioid variant of this entity which closely mimics high grade prostate cancer where I have seen several cases overdiagnosed as a Gleason score 5+5=10. This again reinforces the caution that one should have in diagnosing adenocarcinoma of the prostate in an inflamed gland. However, in this case the findings are diagnostic of adenocarcinoma despite the associated inflammation.

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