LB-54 The Drosophila Notum gene, which is regulated by the Wingless pathway, encodes a secreted hydrolase that modifies heparan sulfate proteoglycans. Our comparative analysis of gene expression in primary human hepatocellular carcinomas (HCCs) and normal organs, including liver, showed that the human ortholog of the Drosophila Notum was markedly overexpressed in a subset of HCCs. We investigated the regulation of NOTUM expression in HCC, focusing on the status of the Wnt pathway because Drosophila Notum is regulated by Armadillo, an ortholog of human beta-catenin. Intracellular beta-catenin was observed in 10 of 40 HCCs by immunohistochemistry (cytoplasmic staining in 1 cases, nuclear staining in 9 case), while membrane-bound beta-catenin was observed in the remaining 30 HCCs. Sequence analysis of CTNNB1 exon 3 revealed 11 HCC cases with somatic missense mutations. Ten of the 11 mutant cases exhibited intracellular beta-catenin staining (nuclear or cytoplasmic), while one mutant case exhibited membrane staining. Overexpression of NOTUM was associated with intracellular beta-catenin localization (10 of 10 cases), but was observed in only 2 of 30 HCCs with membrane staining (6.7%; P