A 49-year-old man with elevated serum PSA underwent prostate needle biopsies. Representative tissue sections were submitted.

Sections revealed patchy proliferations of cells showing mild variation in size and shape situated within the periprostatic tissue (Figure 1). Cells have clear to amphophilic staining cytoplasm, occasionally vacuolated. Admixed inflammatory cells including eosinophils were present and no mitotic figure were observed (Figures 2 and 3). Of the immunostains performed (CK34βE12, p63, racemase, CKAE1/AE3, CD68, PSA, S100, HMB45 and Actin), only CD68 was positive (Figure 4).

The differential diagnosis considerations include:

• Angiomyolipoma (Figure 5)
• Solitary fibrous tumor (Figure 6)
• Poorly differentiated prostatic adenocarcinoma
• Schwannoma
• Xanthogranuloma

Extraprostatic xanthogranuloma

Key Features:

• Rare
• Idiopathic
• In older man
• Incidental finding in patients undergoing TUR or needle biopsy
• Microscopically: proliferations of cells with clear to amphophilic staining cytoplasm admixed with inflammatory cells. No mitotic figures are observed
• CD68 is positive, confirming the histiocytic nature of the lesion

Angiomyolipoma ( AML) (Figure 5): HE 200X This rare tumor has primarily been described in the kidney. However, surgical pathologists have identified this tumor in numerous other organs (heart, colon, lung, nasal cavities, ovary, parotid gland, skin, spermatic cord, bladder, uterus, vagina). This tumor exhibits a collection of blood vessels, smooth muscle, and mature adipose tissue. AML is seen in two distinct clinical settings: sporadic (isolated) or in association with tuberous sclerosis. Although exact figures are difficult to obtain, the sporadic form accounts for approximately 80%-90% of cases of AML. The two forms vary to some degree in their imaging features but are histologically indistinguishable. Immunohistochemical studies have shown that AMLs express the melanocytic markers HMB-45, MART-1 (Melan A), and tyrosinase, in addition to smooth muscle actin.

Solitary fibrous tumor (Figure 6): HE 400X The tumor is grossly well-circumscribed in the prostatic parenchyma. It is variable in cellularity, consisting of a mixture of haphazard, storiform, or short fascicular arrangements of bland spindle cells and less cellular dense collagenous bands. A haemangiopericytoma-like growth pattern is typically seen. Immunostaining for CD34, bcl-2 and CD99 confirms the diagnosis.

Poorly differentiated prostatic adenocarcinoma: Poorly differentiated prostatic adenocarcinoma (Gleason score of 8-10) is characterized by fusion of acini (Gleason pattern 4), with ragged infiltrating cords and nests at the edges, consisting of an anastomosing network or spongework of epithelium.

Gleason pattern 5 is characterized by fused sheets and masses of haphazardly arranged acini in the stroma, raising the concern for anaplastic carcinoma or sarcoma. Up to 1.6% of poorly differentiated prostate cancers will be negative for both PSA and PAP.

Schwannoma: Schwannoma is a rare finding within the prostate. Patients have a mean age of 37 years. The most common sign at presentation is a palpable genital mass accidentally discovered by the patient or detected by the physician during a physical check. The tumor consists of compact spindle cells with vacuolated nuclei, inconspicuous nucleoli and indistinct cytoplasmic borders. These cells are arranged in interlacing fascicles with or without nuclear palissading. There is no necrosis or mitotic figures. Immunostains for protein S-100 is positive, and CD34, bcl-2, Desmin and Actin are negative.

Xanthoma (xanthogranuloma): This is a rare form of idiopathic granulomatous prostatitis that consists of a localized collection of cholesterol-laden histiocytes; it may also be seen in patients with hyperlipidemia. It is usually an incidental finding in patients undergoing transurethral resection or needle biopsy, although it may appear as a palpable nodule. Microscopically, the lesion represents isolated, circumscribed, small, nonspecific granulomatous inflammatory nodules. Rare cases contain areas of typical granulomatous prostatitis, and the term xanthogranulomatous prostatitis is appropriate in such cases. Immunostain for CD68 is positive for the fibrohistiocytic cells.

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