A. Schmitt-Graeff 1 , R. Fischer 1 , M. Grosse-Perdekamp 1 , O. Skalli 2 1 Universityhospital Freiburg , 2 Louisiana State University Health Sciences Center, Shreveport Background/Aims: Synemin is an intermediate filaments (IF) protein which affects the motility of several cell types by modulating the dynamic properties of alpha-actinin and F-actin. We have previously shown that synemin is expressed in resident hepatic stellate cells (HSC) and myofibroblasts (MF) in hepatic inflammation and fibrosis. In the present study we evaluated systematically the expression of synemin in a large cohort of western European hepatocellular carcinoma (HCC). Methods: Single and double immunolabelin for alpha-smooth muscle actin (SMA), vimentin, CD31, CD34, CD68, CEA, CD10, cellular retinol-binding protein1 (CRBP-1) and synemin were performed on 75 paraffin-embedded HCCs and 10 controls. Results: Synemin-positive HSCs/ MFs were a hallmark of non-neoplastic fibrotic liver tissue at the border to the neoplastic lesion but were absent from normal controls. Tumour cell plates of the trabecular and pseudoglandular types of HCC were covered by scattered synemin-positive cells outlining sinusoidal structures. A subpopulation of these cells showed features of pericytes while others resembled endothelium. This pattern correlated with the degree of differentiation and was not observed in poorly differentiated HCCs which generally contained rare intratumoral MFs. Conclusion: The presence of synemin-positive HSCs/MFs in the vicinity of HCCs suggests a possible contribution of mesenchymal cells to the promotion of liver carcinogenesis. Since synemin expression is linked to motility, a migration of this cell type into the tumour and a differentiation in vascular mural cells may be implicated in sinusoidal remodeling and the expansion of the neoplastic population.