Primary
adenocarcinoma of the urinary bladder is an uncommon
neoplasm that can be indistinguishable morphologically from colorectal
adenocarcinoma secondarily involving the bladder by direct extension or
metastasis. In the current study, 17 enteric-type primary
adenocarcinomas of the bladder were immunohistochemically examined for the expression of CDX2,
villin and alpha-methylacyl
coenzyme A racemase (AMACR), immunomarkers preferentially expressed in colorectal
adenocarcinoma. For comparison, 17 secondary colorectal
adenocarcinomas involving the bladder, 23 primary colorectal
adenocarcinomas and 14 conventional urothelial
carcinomas were similarly studied. The results show that all 40 (100%) colorectal
adenocarcinomas expressed CDX2 and 39 (98%) expressed
villin. The expression of these two immunomarkers was less frequent in primary bladder
adenocarcinomas, observed in eight (47%) and 11 (65%) cases, respectively (P<0.0001 and P=0.0019, respectively). The frequency of positive AMACR immunostaining was similar between these two types of
tumors, detected in 28 (70%) colorectal
adenocarcinomas and 11 (65%) primary bladder
adenocarcinomas (P=0.694). None of the urothelial
carcinomas exhibited CDX2 or
villin immunoreactivity; and only two (14%) showed positive staining for AMACR. These results demonstrate that CDX2 and
villin are of diagnostic value in aiding in the distinction between primary
adenocarcinoma of the bladder and secondary
colorectal carcinoma. Lack of CDX2 and
villin signals points strongly to a bladder primary.