Correct: B

Histology: Prostate chips with tumor composed of nests of basaloid cells with hyperchromatic nuclei with prominent nucleoli, scant cytoplasm and peripheral palisading. There is an infiltrative growth with spread between benign glands.

Discussion: Basal cell carcinoma of the prostate is rare. Patients with basal cell carcinoma most often present with urinary obstruction and are diagnosed in a transurethral resection rather than in a needle biopsy. Unless basal cell carcinoma is associated with usual acinar carcinoma, they do not elevate serum PSA. The tumor is usually composed of large nests of basaloid cells with hyperchromatic nuclei with prominent nucleoli, scant cytoplasm and peripheral palisading. Mitotic activity can vary greatly. Nests with variable sizes and shapes and with an infiltrative growth pattern helps to differentiate carcinomas from florid basal cell hyperplasia. Necrosis can be present, especially in cases with large nests. Some cases show prominent desmoplastic stroma. A subset of cases are characterized by adenoid cystic-like growth and referred to as adenoid cystic carcinoma. Tumor nests in adenoid cystic carcinomas are characterized by cribriform architecture often with intraglandular hyaline (basement membrane) material. Focal sebaceous and squamous differentiation have been described. In addition to the nested and adenoid cystic patterns, other architectural patterns described include basal cell hyperplasia-like pattern and tubules/cords of cells. The nests or tubules are frequently lined by cells with eosinophilic cytoplasm. The majority of basal cell carcinomas show local invasion including extraprostatic extension and invasion of the bladder neck. In the largest series reported, approximately 10-20% of cases developed distant metastases, and all of them were characterized by large nests with central necrosis. By immunohistochemistry, basal cell carcinomas are positive for high molecular weight cytokeratin (100%), p63 (40-100%), diffusely positive for Bcl-2 and CK7 staining can be seen in luminal cells. Myoepithelial cell markers smooth muscle actin, calponin, smooth muscle myosin heavy chain and S100 are negative. Most cases are negative for PSA. The main differential diagnosis is with florid basal cell hyperplasia and the features are seen in carcinoma but not in hyperplasia include large nests with necrosis, adenoid cystic pattern, variable sizes and shapes of the nests with infiltrating borders, extraprostatic extension or bladder neck invasion, and desmoplastic stromal reaction. Occasionally, basal cell hyperplasia can involve bladder neck muscle or present between normal prostatic glands, therefore these findings should not be considered in isolation, sufficient to make a diagnosis of carcinoma. The differential diagnosis with small cell carcinoma is a consideration when basal cell carcinoma presents large nests with central necrosis; however, small cell carcinoma has a higher proliferation rate, and it is positive for NE markers and negative for p63.

References
1. Osunkoya AO, Hansel DE, Sun X, Netto GJ, Epstein JI. Aberrant diffuse expression of p63 in adenocarcinoma of the prostate on needle biopsy and radical prostatectomy: report of 21 cases. Am J Surg Pathol. 2008;32(3):461-467.
2. Brimo F, Epstein JI. Selected common diagnostic problems in urologic pathology: perspectives from a large consult service in genitourinary pathology. Arch Pathol Lab Med. 2012;136(4):360-371.
3. Brimo F, Epstein JI. Immunohistochemical pitfalls in prostate pathology. Hum Pathol. 2012;43(3):313-324.