Biliary cytokeratin expression but not CD56 (N-CAM) expression aids in the differenzial diagnosis of non-neoplastic bile duct diseases

Introduction: Non-neoplastic bile duct diseases include several entities with a variety of clinical and histopathological features. In needle biopsies, however, these may overlap. Here, auxiliary diagnostic markers would be helpful. CD56 (N-CAM) has been reported in bile duct development, liver regeneration and different liver diseases. Aim: This study was performed to evaluate the diagnostic value of CD56 immunohistochemistry compared to biliary cytokeratins in the diagnosis of non-neoplastic biliary liver diseases in liver needle biopsies. Methods: 38 cases (10x PSC; 10x PBC; 10x obstruction; 8x drug induced liver disease [DILD]) were analyzed using antibodies against CD56/NCAM, CK7 and CK19. Results: Twenty-three of all cases (63.9%) showed a positive CD56 reaction (PSC 6/10; PBC 9/10; obstruction 5/10; DILD 3/8) with no statistical significance between the groups. Biliary cytokeratins visualized the bile ducts in all cases. CK7 highlighted cholangiolar metaplasia in seven cases (3x PSC; 1x PBC; 3c DILD). Conclusion: CD56 can not be used as a supplementary tool in the differenzial diagnosis of non neoplastic biliary diseases. CK7 should be included in the routine assessment of liver biopsies in these settings. Further research is needed to find better targets for immunohistochemical determination of the etiology of bile duct damage.