Cytokeratin 7 and 20 Expression in Cholangiocarcinomas Varies Along the Biliary Tract But Still Differs From That in Colorectal Carcinoma Metastasis

In the liver, the immunostaining of cytokeratins (CK) 7 and 20 has been used to distinguish usual peripheral cholangiocarcinomas (CC) and colorectal carcinoma metastasis (CRM). However, other subtypes of CC are not infrequent and may be particularly difficult to distinguish from CRM by histology and even immunohistochemistry. Therefore, 48 CC from different locations, either peripheral (n = 19), or nonperipheral, that is, from the large intrahepatic bile ducts, the hilum, and the extrahepatic bile ducts (n = 29), and with different cytoarchitectural patterns were tested for CK7 and CK20 and compared with 31 CRM. CC were positive for CK7 and CK20 in 96% and 70%, respectively, whatever the architecture and differentiation of the tumor. The labeling index (LI) of CK7 in CC was always high, whereas it was low or moderate for CK20. CK20-positive phenotype was significantly more frequent in nonperipheral than in peripheral CC (82% vs 47%; p = 0.007). CRM were all positive for CK20 with a high LI, and mostly negative (81%) for CK7. In conclusion, (1) the CK immunoprofile of CC varies according to the location of the tumor in the biliary tract, peripheral CC being more often CK7+/CK20-, and nonperipheral ones CK7+/CK20+; and (2) a decision tree based on CK20 LI and CK7 positivity allows the distinction of CRM and CC, even for the nonperipheral type.