To investigate the expression of inhibitor of differentiation-1 (Id-1) in hepatocellular carcinoma (HCC) and its mechanism in tumor metastasis.

Tissue specimens were collected from 56 HCC patients undergoing hepatectomy in the First Affiliated Hospital of Nanchang University from January 2014 to December 2016. The informed consents of all patients were obtained and the local ethical committee approval was received. Among them, 41 patients were male and 15 female, aged 26-79 years with a median age of 55 years. The para-carcinoma liver tissues from 45 cases and normal liver tissues from 21 healthy subjects were used as controls. The expression levels of Id-1, E-cadherin, Vimentin and MMP-9 were quantitatively measured by immunohistochemistry. The positive rates between two groups were compared by Chi-square test. Spearman's rank correlation analysis was performed.

In HCC tissues, the positive rates of Id-1, E-cadherin, Vimentin and MMP-9 expression were 86%(48/56), 75%(42/56), 39%(22/56) and 84%(47/56), significantly higher compared with 62%(41/66), 33%(22/66), 15%(10/66) and 47%(31/66) in control group (χ²=8.57, 13.62, 10.73, 11.08; P<0.05). The positive rate of Id-1 in patients with tumor diameter >5 cm was 100%(24/24), significantly higher than 75%(24/32) in patients with tumor diameter≤5 cm. The positive rate of Id-1 in patients with tumor metastasis was 97%(34/35), significantly higher than 66%(14/21) in patients without tumor metastasis (χ²=9.25, 10.24; P<0.05). The expression level of Id-1 was negatively correlated with the degree of HCC differentiation (r_s=-0.295, P<0.05). The expression level of Id-1 was negatively associated with the expression of E-cadherin and MMP-9 (r_s=-0.432, -0.326; P<0.05), whereas positively correlated with the expression of Vimentin (r_s=0.713, P<0.05).

Id-1 is highly expressed in HCC tissues probably by inducing epithelial-mesenchymal transition and degrading extracellular matrix, thereby promoting the invasion and metastasis of HCC.