As salivary gland tumors have variable histological and biological characteristics, appropriate pathological diagnosis is necessary. We collected and reviewed 551 cases of salivary gland tumors which were surgically operated from 1983 to 2007 (24 years). The 551 cases were comprised of 537 epithelial tumors (97.5%), 10 hematolymphoid tumors and 4 mesenchymal tumors. The epithelial tumors were located in the parotid gland (475 cases) and submandibular gland (62 cases). Malignancies accounted for 123 (22.9%) of the 537 epithelial tumors. The frequency of malignancies was much higher in the submandibular gland (45.2%) than in the parotid gland (20%). The frequent histological types among all epithelial tumors were pleomorphic adenoma (285 cases; 53.1%), followed by Warthin's tumor (19.4%), and those among malignant epithelial tumors (carcinomas) were adenoid cystic carcinoma (25 cases), mucoepidermoid carcinoma (17) and carcinoma ex pleomorphic adenoma (15). The risk of malignant change of pleomorphic adenomas was estimated as 5% (15/300 cases). The histological subtypes of carcinoma ex pleomorphic adenoma varied among the cases, and in some cases were salivary duct carcinoma, which is a high-risk carcinoma that requires careful attention.
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