Immunohistochemical distribution of CD9 in parotid gland tumors

Objective: CD9 is a member of the tetra-membrane-spanning glycoprotein family called tetraspanin. CD9 suppresses breeding and motion in some types of cancer cells. At present, the expression of CD9 in the salivary gland has not yet been elucidated. Methods: We examined the expression of CD9 not only in the normal salivary glands of human embryo and adults but also in the parotid gland tumors using immunohistochemical staining. Results: CD9 was not detected in embryos at 18 weeks of gestation, but was observed at 24 weeks in the salivary gland. CD9 was constantly detected in the adult normal parotid gland. In benign parotid gland tumors, CD9 was present in the 11 of 16 pleomorphic adenomas, every Warthin tumors (18/18) and basal cell adenoma (1/1). In contrast, positive staining for CD9 in malignant parotid tumors was observed in only the case of mucoepidermoid carcinomas. Neither acinic cell carcinomas or adenoid cystic carcinomas did show positive reaction in examined cases. The localization of CD9 was also observed in intercalated duct cells. Conclusion: There was a statistically significant reduced expression of CD9 in malignant parotid gland tumors as compared to benign parotid gland tumors (P=0.003).