AIM: To investigate the molecular pathways involved in human cholangiocarcinogenesis by gene expression profiling.METHODS: Oligonucleotide arrays (Affymetr/x U133A)were used to establish a specific gene expression profile of intrahepatic CCC in comparison to corresponding nonmalignant liver tissue.To validate the expression values of the most overexpressed genes, RT-PCR experiments were performed.RESULTS: Five hundred and fifty-two statistically differentially expressed genes/ESTs (221 probes significantly up-regulated, 331 probes down-regulated;P2;≥70%) were identified.Using these data and two-dimensional cluster analysis,a specific gene expression profile was obtained allowing fast and reproducible differentiation of CCC, which was confirmed by supervised neuronal network modelling.The most consistently overexpressed gene (median fold change 33.5, significantly overexpressed in 100%)encoded osteopontin.Furthermore, an association of various genes with the histopathological grading could be demonstrated.CONCLUSION: A highly specific gone expression profile for intrahepatic CCC was identified, allowing for its fast and reproducible discrimination against nonmalignant liver tissue and other liver masses.The most overexpressed gene in intrahepatic CCC was the gene encoding osteopontin.These data may lead to a better understanding of human cholangiocarcinogenesis.