Background: Epithelial-mesenchymal transition (EMT), when epithelial cells convert to mesenchymal cells, influences cancer invasion and metastasis. Smad interacting protein 1 (SIP1) is an EMT trigger, which is inversely correlated with E-cadherin in some carcinomas. To elucidate the role of SIP1 in esophageal squamous cell carcinoma (ESCC), the status of EMT and the clinicopathological features were evaluated. Methods: Immunohistochemical (IHC) analyses of 111 human ESCC tissue specimens for SIP1 and E-cadherin were performed, and the relationships between the expression and clinicopathological features were evaluated. Results: IHC analyses of esophageal tumors showed the expression of SIP1 and E-cadherin to be significantly inversely correlated. Significant correlations between the SIP1 expression and clinicopathological variables such as differentiation, depth of invasion, vascular invasion, and pathological stage were also seen. Conversely, tumors with a weak expression of E-cadherin tended to exhibit greater histological differentiation. Logistic regression analyses revealed a positive SIP1 expression, lymphatic invasion, and vascular invasion to be factors predicting lymph node (LN) metastasis. Univariate survival analyses revealed a positive SIP1 expression predicted a poorer overall survival than a negative expression. Conclusion: These results suggest that SIP1 is correlated with LN metastasis and may therefore be an independent marker for metastasis in patients with ESCC.
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