Immunohistochemical demonstration of epithelial glutathione S‐transferase isoenzymes in normal, benign, premalignant and malignant human oral mucosa

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Abstract
The expression and localization of glutathione S-transferase (GST) isoenzymes in the epithelium of normal oral mucosa (n = 9), overlying reactive fibrous hyperplasia (n = 9), and of potentially malignant [leukoplakia (n = 25), submucous fibrosis (n = 12), verrucous hyperplasia (n = 16)] and malignant [squamous cell carcinoma (n = 36), verrucous carcinoma (n = 13)] oral lesions were examined immunohistochemically using polyclonal antibodies raised against GST isoenzymes (alpha, mu and pi) with the standard avidin-biotin-peroxidase complex (ABC) method. GST alpha, mu and pi were almost completely absent in the epithelium of normal oral mucosa and overlying benign fibrous tissues. GST alpha staining was cytoplasmic and focally positive, while GST mu staining was similar to but weaker than that seen for GST alpha. GST pi showed both cytoplasmic and nuclear staining and was expressed in 60% of leukoplakias with mild dysplasia (n = 15), 80% of leukoplakias with moderate to severe dysplasia (n = 10). 75% of submucous fibrosis samples (n = 12), 75% of verrucous hyperplasias (n = 16), 77% of verrucous carcinomas (n = 13), 81% of well-differentiated squamous cell carcinomas (n = 26) and 70% of moderate- to poorly-differentiated squamous cell carcinomas (n = 10). In addition, GST pi expression was independent of the state of differentiation of oral cancers. Since GST pi was significantly over-expressed in the oral premalignant and malignant lesions, the kinetics of GST pi-positive cells and the value of GST pi as a tumor marker in oral carcinogenesis need further investigation.