Intraductal papillary cholangiocarcinoma and atypical biliary epithelial lesions confused with intrabiliary extension of metastatic colorectal carcinoma.

Intrabiliary metastasis of colorectal carcinoma is not infrequent. We demonstrated interesting intraductal biliary epithelial lesions in two cases of colorectal carcinoma. The first case (65-year-old female) presented intrahepatic papillary adenocarcinoma with intrabiliary extension. While this biliary carcinoma was once diagnosed as intrabiliary metastasis of colon carcinoma, these carcinoma cells were positive for cytokeratin 7 (CK7, biliary cytokeratin) and negative for CK20 (intestinal cytokeratin). In addition, these carcinoma cells were oncocytic. Finally, a diagnosis of intraductal papillary cholangiocarcinoma of oncocytic variant was made. In the second case (74-year-old male), atypical biliary epithelial lesions were found near intrabiliary metastasis of colon carcinoma. The atypical lesions were immunohistochemically positive for CK7 but negative for CK20, and negative for p53. On the contrary, intraductal metastatic carcinoma was totally reversed, suggesting that atypical biliary lesions were not metastatic. Survey of such atypical biliary lesions in 6 consecutive cases with intrabiliary metastasis from colon carcinoma including this case disclosed that one third of such cases revealed such atypical biliary lesions. A variable type of biliary lesions should be carefully differentiated from intrabiliary metastatic colorectal carcinoma and a combined immunohistochemistry of CK7 and CK20 is useful for this differentiation.