Thesis (M.Sc.)--Chulalongkorn University, 2011

Mucoepidermoid carcinoma (MEC), malignancy of salivary gland, can be classified into low-, intermediate-, and high-grade tumors based on its histological features. The proportion of cellular components or the presence of a cystic component, neural invasion, necrosis, mitotic activity and anaplasia are used. However, none of the system has not been universally accepted. Methylation levels of long interspersed nuclear element-1 (LINE-1) and Alu elements reduce in cancerous tissue and relate to the severity of some cancers. However, there has been no study of LINE-1 and Alu methylation in MEC tissues. This study investigated LINE-1 and Alu element methylation in MEC by using combined bisulfite restriction analysis. MEC tissue showed a significantly lower level of LINE-1 and Alu element methylation overall compared to the normal salivary gland tissue. These levels were also significantly different between cell types and showed a stepwise decrease from the adjacent normal salivary gland to the intermediate, mucous and squamous cells. In addition, the percentage of hypermethylation pattern of LINE-1 and hypomethylation pattern of Alu were significantly difference between MEC and normal salivary gland tissue. Moreover, the reduced methylation levels of LINE-1 were correlated with poorer histological grades. The results suggested that the proportion of cells may be important for MEC classification. LINE-1 and Alu elememt methylation levels and patterns may be useful for accurate MEC diagnosis and prognostic prediction, which can improve survival rates and quality of life of patients.