KAI1 is a tumor suppressor gene originally identified in prostate cancer. Recent studies of oral cancer, including our investigations, have shown frequent down-regulation of KAI1 expression in many tumor types, whereas mutation of the gene is infrequent. However, the role of the down-expression of KAI1 in oncogenesis and the progression of oral carcinoma remains unclear. In this study, we analyzed the mutational status of KAI1 and both the mRNA and protein levels of the gene in a series of gingival carcinomas and precancerous lesions (20 leukoplakias, 50 squamous cell carcinomas, and 20 lymph node metastatic tumors) . Although no mutation was found in any sample tested, immunohistochemical studies revealed high frequencies of KAI1 down-regulation not only in the metastatic tumors (20 of 20, 100 %) , but also in the primary carcinomas (39 of 50, 78 %) and leukoplakias (9 of 20, 45 %). Down-regulation of KAI1 protein expression was significantly related to carcinogenesis and metastasis (precancerous lesions, primary carcinomas, and metastatic tumors) (p<0.001) as well as to lymph node metastasis (p=0.0022). RT PCR analysis confirmed these results. Therefore, suppressed expression of KAI1 was suggested to play clinically significant roles in carcinogenesis and lymph node metastasis .
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