The differential diagnosis between poorly differentiated prostate adenocarcinoma (PAC) involving the bladder and high-grade urothelial bladder cancer (UC) with prostate extension can be very challenging. The aim of this study is to evaluate the use of a panel of antibodies to distinguish the poorly differentiated forms of these two tumors. We evaluated a series of 40 PAC cases (Gleason's grade >/= 8) and 45 (G3) UC cases obtained from transurethral endoscopic resection material. Immunohistochemical analysis was performed using the following antibodies: prostate acid phosphatase (PAP), prostate-specific antigen (PSA), uroplakin III (UP), thrombomodulin (TM), cytokeratin (CK) 7, and CK20. PAC expressed PSA and PAP in 34 and 38 cases, respectively. The sensitivity and specificity of expressing at least 1 marker (PSA+ or PAP+) is 95% and 100%, respectively. All UC cases were negative for both markers. UC expressed UP and TM in 27 and 22 cases, respectively. In addition, 36 of 45 cases stained positively for at least 1 marker (UP + or TM +) with specificity and sensitivity of 80% and 100%, respectively. All cases of PAC were negative for both markers. Twenty-eight UC cases were CK7+/CK20 +, and 4 PAC cases stained positively for both markers. On the other hand, 29 PAC cases and 4 UC cases were CK7-/CK20-. We concluded that PSA, PAP, UP, and TM are very useful markers in differentiating poorly differentiated UC from PAC. Finally, when all 4 markers (PAP, PSA, UP, and TM) were negative, CK7 and CK20 appeared of no major use in making the differential diagnosis.
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