الفهرس 
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Abstract
Tumors of the salivary gland are uncommon head and neck neoplasia, representing only 3-6% of them. These neoplasms composed heterogeneous group of tumors with variable histological pictures.
Metallthioneins (MTs) are member of Non-enzymatic polypeptides proteins which are first isolated in 1957 as a cadmium (CD)-binding protein in the horse kidney. The most common metallothioneins are (MT I and MT II). They are expressed in most tissues and have been localized largely in cell cytoplasm, lysosomes, mitochondria and nuclei.
The major physiological function of MTs includes homeostasis of essential metals (Zinc and copper) which may be required for the cell growth and differentiation, protection against cytotoxicity of cadmium and other toxic metals, scavenging free radicals generated in oxidative stress, antiapoptotic effect, anigogenesis, immune defense responses and cell cycle progression and cell differentiation. Howvere the role of MTs in oncogenesis is still unclear.
Previous studies have demonstrated expression of MTs in various types of human tumors such as nasopharynx, breast, prostate, kidney, lung, pancreatic cancer, endometrial, ovary, , urinary bladder, cervical and skin. In some cases MT-II expression correlate with tumor grade/stage, chemotherapy/ radiation resistance, and poor prognosis. In contrast, decreased MT-I+II expression is associated with poor prognosis in human hepatic, prostate, thyroid, central nervous system and testicular tumors
The aim of this research was to assess metallothionein (MT) expression with immunohistochemical localization in benign and malignant salivary gland tumors and to compare metallothionein (MT) expression among the different histological patterns of salivary gland tumors.
Fourty cases of salivary gland tumors were included in this study. The biopsies were histologically examined after hematoxlin and eosin staining. Clinical data of these cases were collected. The sample included eight cases of benign salivary gland tumors (five cases of pleomorphic adenoma, myoepithelioma, warthin’s tumor as well as basal cell adenoma were represented by one case each), and thirty-two cases of malignant salivary gland tumors (nine cases of mucoepidermoid carcinoma, seven cases of carcinoma ex pleomorphic adenoma, six cases of adenoid cystic carcinoma, five cases of myoepithelial carcinoma, two cases of acinic cell carcinoma and one case of each of oncocytic carcinoma, salivary duct carcinoma and polymorphous low grade adenocarcinoma.
The malignant tumors (80%) were more common than the benign tumors (20%), the most common salivary gland tumor was the mucoepidermoid carcinoma and represented 22.5%. carcinoma ex pleomorphic adenoma came second in order representing 17.5%. Adenoid cystic carcinoma came third in order representing 15%. The median age for patients in this work was 45 years (with wide range from11 -81 years). Out of 40 cases, (62.5%) were female and (37.5%) were males. As regards to location, the parotid gland was the most common site, followed by the palate.
As for immunohistochemical detection of metallothionein protein; All tumors analyzed, benign and malignant tumors showed a positive metallothionein expression with different intensity. Normal salivary gland tissue showed positive immunoreactivity for metallothionein, in the ductal epithelial cells and also in myoepithelial cells lining the acini periphery.
The intensity of immunostaining of metallothionein between benign and malignant salivary gland tumors was calculated. There was a statistically significant difference (P < 0.05) in the MOD which was 81.60 and 38.87 for malignant and benign salivary gland tumors, respectively. The difference in MA% between these two groups were also higher in malignant than benign tumors and also reached a significant value.
The difference in mean area percent of metallothionein expression between low-grade and high-grade MEC was calculated. The mean area percent was higher in high -grade type compared to the low grade one. A significant difference (P < 0.05) was found. Also mean optical density was higher in high-grade compared to low-grade but with no significant difference.