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Salivary gland tumors are a morphologically and clinically diverse group of neoplasms, which may present significant diagnostic and management challenges. These tumors are rare, with an overall incidence in the Western world of approximately 2.5 cases to 3.0 cases per 100,000 per year. Malignant salivary gland neoplasms account for more than 0.5% of all malignancies and approximately 3% to 5% of all head and neck cancers.[1,2] Most patients with malignant salivary gland tumors are in the sixth or seventh decade of life.[3,4] Although exposure to ionizing radiation has been implicated as a cause of salivary gland cancer, the etiology of most salivary gland cancers cannot be determined.[2,3,5,6] Occupations associated with an increased risk for salivary gland cancers include rubber products manufacturing, asbestos mining, plumbing, and some types of woodworking.
Tumors of the salivary glands comprise those in the major glands (e.g., parotid, submandibular, and sublingual) and the minor glands (e.g., oral mucosa, palate, uvula, floor of mouth, posterior tongue, retromolar area and peritonsillar area, pharynx, larynx, and paranasal sinuses).[2,7] Minor salivary gland lesions are most frequently seen in the oral cavity.
Of salivary gland neoplasms, more than 50% are benign, and approximately 70% to 80% of all salivary gland neoplasms originate in the parotid gland.[1,2,8] The palate is the most common site of minor salivary gland tumors. The frequency of malignant lesions varies by site. Approximately 20% to 25% of parotid tumors, 35% to 40% of submandibular tumors, 50% of palate tumors, and more than 90% of sublingual gland tumors are malignant.[1,9]
Histologically, salivary gland tumors represent the most heterogenous group of tumors of any tissue in the body. Although almost 40 histologic types of epithelial tumors of the salivary glands exist, some are exceedingly rare and may be the subject of only a few case reports.[1,11] The most common benign major and minor salivary gland tumor is the pleomorphic adenoma, which comprises about 50% of all salivary gland tumors and 65% of parotid gland tumors. The most common malignant major and minor salivary gland tumor is the mucoepidermoid carcinoma, which comprises about 10% of all salivary gland neoplasms and approximately 35% of malignant salivary gland neoplasms.[1,12] This neoplasm occurs most often in the parotid gland.[2,12,13] This type and other histologic types of salivary gland neoplasms are reviewed in detail in the Cellular Classification of Salivary Gland Treatment section of this summary.