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Objective: To detect the differences in the expression levels of protein and mRNA of E-cadherin and β-catenin in primary tumor and lymph node metastatic tumor of nasopharyngeal carcinoma (NPC),and to investigate the mechanism of invasion and metastasis of neoplastic cell in NPC. Methods: 21biopsies taken from primary tumor and another 21 biopsies from lymph node metastatic tumor of NPC were collected from the affiliated hospitals of Sun Yat-sen University of Medical Sciences during 1999-2002.Weste blotting assay, immunohistochemical staining and reverse transcriptase-polymeraes chain reaction (RT-PCR) were adopted to detect the expression levels of protein and mRNA of E-cadherin and β-catenin in all of 42 samples. Results: (1) In 21 cases of lymph node metastatic tumor, the protein expression level of E-cadherin was lower detected by immunohistochemical staining (50% in average) and Weste blotting (RI: 65±15.9 in average) than that in primary tumor of NPC (80% and 206.7±32.7 in average respectively). Furthermore, mRNA expression level of E-cadherin was also lower in metastatic tumor than that in primary tumor, with the difference being significant (P＜0.05). (2) Both primary NPC and lymph node metastatic NPC were found to have high β-catenin protein and mRNA expression with the differences being not statistically significant (P＞0.05). (3) There was no correlation between neoplastic cell expression ofβ-catenin and E-cadherin either in primary tumor or in lymph node metastatic tumors. Conclusion:Down-regulation of the expression of E-cadherin may play a critical role in neoplastic cell invasion and metastasis in NPC.