الفهرس 
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Abstract
Background: Thyroid cancer (TC) is the most common type of malignant endocrine cancer and it’s ranked as the 10th most common cancer worldwide, accounting for ∼5% of all thyroid nodules and its incidence increases, due to improvement of diagnostic procedures leading to early detection. In Egypt, it’s considered the 5th most common cancer in Egypt and 2.3% of all malignancies. The majority of Papillary thyroid cancer (PTC) comprises classic and follicular variant (FV-PTC) histologic subtypes. PTC is the most frequent type of differentiated thyroid carcinoma. In Egypt PTC subtype represents 85% of all TC cases. The most important risk factor of PTC is radiation exposure, it is proven to increase the chance of malignancy of thyroid gland from 5% to 50%. Genetic predisposition has been proven to develop PTC as it runs in families in 5% of cases. PTC is associated with excellent disease-specific survival (DSS) of more than 90%. SIX1 is expressed in a wide range of normal and neoplastic tissues and it has different pathways in tumorigenesis in different tissues, including induction of epithelial mesenchymal transition (EMT), increased proliferation and independent growth by activating cyclin A1, SIX1 was upregulated in human thyroid cancer cell and promoted cell proliferation and invasion. However, few report described the role of SIX1 in TC, especially PTC, and its possible relation with tumor behavior.
Aim of the work: this study was conducted to research the role of SIX1 in PTC, and its possible relation with tumor behavior and the clinicopathological features of PTC.
Material and Methods: Immunohistochemical staining of SIX1 was conducted on 50 randomly chosen tissue specimens of papillary thyroid carcinoma, 34 (68%) were classic PTC and 16 (32%) were follicular subtype, that was done by using the avidin biotin-peroxidase complex method with diaminobenizidine (DAB) chromogen detection system.
Results: High SIX1 expression was detected in 36% of cases. SIX1 expression showed statistically significant correlation with tumor focality (P= 0.003), lymph node metastasis (P= 0.002), tumor grade (P= 0.002), advanced tumor stage (P= 0.01) assessed by pT staging system, tumor necrosis (P= 0.002), lympho-vascular, perineural invasion and extra thyroidal extension (P= 0.002), (P= 0.01) and (P= 0.001) respectively. No significant associations were observed between SIX1 expression and patients’ age, gender, tumor site, tumor size or histological subtype. High SIX1 expression was observed in 38.2% (13/34) of classic PTC versus 31.3% (5/16) in Follicular variant PTC (FV-PTC) cases.