Liver-intestine cadherin (LI-cadherin) represents a novel type of cadherin within the cadherin superfamily that comprises seven cadherin repeats and a short cytoplasmic domain. In this study, we first examined LI-cadherin expression immunohistochemically in 34 specimens of human intrahepatic cholangiocarcinoma (ICC). LI-cadherin expression was positive (defined as positivity in > or = 10% of cells) in 18 of the ICCs (52.9%). LI-cadherin negativity was significantly correlated with tumor dedifferentiation (P=0.026) and vascular invasion (P=0.015). The cumulative survival rate of patients with LI-cadherin-negative ICC was significantly shorter than that of patients with LI-cadherin-positive ICC (P=0.021). Multivariate analysis identified the extent of LI-cadherin staining as an independent prognostic factor for ICC survival (P=0.027). Next, to elucidate the mechanism of loss of LI-cadherin-mediated aggressiveness in ICC, we knocked down LI-cadherin expression in an ICC cell line using small interfering RNA (siRNA) technology, and screened for genes that were expressed differentially between these cells and ICC cells transfected with scrambled siRNA using microarray analysis with real-time polymerase chain reaction confirmation. Among 21 identified genes, we focused on metal-responsive transcription factor-1 (MTF-1), whose target genes might contribute to tumor aggressiveness. Expression of placental growth factor (PlGF), one of the MTF-1 target genes, was up-regulated in the ICC cells transfected with LI-cadherin siRNA. Likewise, PlGF expression was up-regulated in LI-cadherin-negative ICC specimens. There was a significant inverse relationship between these expressions (P=0.033). Furthermore, the microvessel density of LI-cadherin-negative ICC specimens was higher than that of LI-cadherin-positive specimens. These findings suggest that loss of LI-cadherin in ICC is associated with tumor dedifferentiation and vascular invasion, and thus poor prognosis. Loss of LI-cadherin results in up-regulation of MTF-1 and PlGF, thereby regulating angiogenesis in ICC.