الفهرس 
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Abstract
Oral squamous cell carcinoma (OSCC) is the most common malignant epithelial tumor in the oral and maxillofacial region as it accounts for nearly 95% of all the head and neck cancers. Despite, OSCC is epithelial tumor, its cells undergo an epithelial–mesenchymal transition (EMT) by losing their adhesion and acquire the structural and functional characteristics of mesenchymal cells, leading to the upregulation of cell migration and the promotion of tumor cell dissemination. Therefore, EMT attracted broad attention due to its close relationship with cancer invasion and metastasis. Therefore, the current study was directed to clarify the role of cadherin switching from E-cadherin to N-cadherin expression, which is very important for cell invasion, progression; migration &metastasis of OSCC. In addition to clarify if there is any genetic alteration leads to the epithelial cell transfer into motile cells by EMT in OSCC cell line. This study included thirty formalin-fixed, paraffin-embedded tissue blocks of OSCC. They involved 6 cases exhibited lymph node metastasis. They were collected from the archived files of patients at Oral Pathology Department, Faculty of Dentistry, Tanta University. The lymph nodes metastatic OSCC cases were obtained from Nasser Cancer Institute. The OSCC specimens were categorized into three groups, ten specimens for each group representing well differentiated, moderately differentiated and poorly differentiated squamous cell carcinomas. They were stained with H&E as well as immunohistochemically stained with antibodies against E- and Ncadherins. Cell cultures were performed using OSCC cell lines (SCC-15/ SCC-25) from human tongue. F-12K medium (Kaighn’s Modification of Ham’s F12 Medium) was added as EMT inducing media. Real time polymerase chain reaction (RT-PCR) was used to identify E- and N-cadherins mRNA gene expression levels. The present findings revealed the expression of E cadherin in normal epithelial tissue and did not express N-cadherin in control sections. Cadherin switching appears in early invasive OSCC with normal expression of E-cadherin and presence of focal positive stained cells for N-cadherin in the underlying connective tissue at the invasive area. In cases of OSCC presented clinically as leukoplakia; N-cadherin expression decreased, however, E-cadherin expression increased. In cases of erythroplakic OSCC; a moderate E-cadherin staining and intense N- cadherin were recorded. Cadherin switching was clearly observed in OSCC appeared as ulcer as well as in cases of poorly differentiated OSCC. These cases displayed reduction of E cadherin with increased N-cadherin expression. ON contrary, in poorly differentiated OSCC; cases of well differentiated OSCC displayed more E-cadherin expression. Cases of OSCC with regional lymph node metastasis also showed cadherin switching. There was statistical significance difference in immune reactive scoring (IRS) of E and N-cadherin in all cases of OSCC. Also, there was a significant correlation detected between E and N-cadherin gene expression in cell cultures with using F-12K medium as EMT inducing media. Therefore, expression of both E- and N-cadherins are considered as accurate progressive and metastatic markers of OSCC.