Immunohistochemistry in the differential diagnosis between primary and secondary intestinal adenocarcinoma of the urinary bladder.

Distinguishing between primary adenocarcinomas and secondary colonic adenocarcinomas of the urinary bladder is often difficult because they appear morphologically similar but invariably require different treatment strategies. The aim of the study was to define the utility of a limited immunohistochemical panel consisting of CDX-2, cytokeratins 7 (CK7) and 20 (CK20), and carcinoembryonic antigen (CEA) in differentiating primary from secondary bladder adenocarcinomas. Formalin-fixed, paraffin-embedded tissues from 8 primary bladder adenocarcinomas and 23 colorectal adenocarcinomas involving the bladder were included in the study. Statistical analysis was performed using the Fisher exact test. The majority (87.5%) of primary bladder adenocarcinomas were CDX-2 negative, and only one case of primary bladder adenocarcinoma was positive, while CDX-2 was strongly expressed in the nucleus of all cases of secondary (colonic) bladder tumor (P < 0.0005). Five cases (62.5%) of primary bladder adenocarcinoma and one case (4.3%) of secondary bladder tumor showed positive staining for CK7 (P = 0.002), whereas CK20 showed positive staining in five cases (62.5%) of primary bladder adenocarcinoma and in all the secondary bladder tumors (P = 0.012). All 23 secondary bladder tumors and 7 primary bladder adenocarcinomas (87.5%) expressed CEA (P = 0.25). These data demonstrate that a restricted immunohistochemical panel consisting of CDX-2, CK7, CK20, and CEA may be of use in differentiating primary bladder adenocarcinoma from secondary adenocarcinoma of colorectal origin.