General Information About Salivary Gland Cancer
Note: Other PDQ summaries containing information related to salivary gland cancer include the following:
- Hypopharyngeal Cancer Treatment
- Laryngeal Cancer Treatment
- Lip and Oral Cavity Cancer Treatment
- Nasopharyngeal Cancer Treatment
- Paranasal Sinus and Nasal Cavity Cancer Treatment
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.
Most patients with benign tumors of the major or minor salivary glands present with painless swelling of the parotid, submandibular, or the sublingual glands. Neurological signs, such as numbness or weakness caused by nerve involvement, typically indicate a malignancy. Facial nerve weakness that is associated with a parotid or submandibular tumor is an ominous sign. Persistent facial pain is highly suggestive of malignancy; approximately 10% to 15% of malignant parotid neoplasms present with pain.[8,14] (Refer to the PDQ summary on Pain for more information.) The majority of parotid tumors, both benign and malignant, however, present as an asymptomatic mass in the gland.[2,8]
Early-stage low-grade malignant salivary gland tumors are usually curable by adequate surgical resection alone. The prognosis is more favorable when the tumor is in a major salivary gland; the parotid gland is most favorable, then the submandibular gland; the least favorable primary sites are the sublingual and minor salivary glands. Large bulky tumors or high-grade tumors carry a poorer prognosis and may best be treated by surgical resection combined with postoperative radiation therapy. The prognosis also depends on the following:[16,17]
- Gland in which they arise.
- Grade (i.e., degree of malignancy).
- Extent of primary tumor (i.e., the stage).
- Whether the tumor involves the facial nerve, has fixation to the skin or deep structures, or has spread to lymph nodes or distant sites.
Overall, clinical stage, particularly tumor size, may be the crucial factor to determine the outcome of salivary gland cancer and may be more important than histologic grade.
Perineural invasion can also occur, particularly in high-grade adenoid cystic carcinoma, and should be specifically identified and treated. Radiation therapy may increase the chance of local control and increase the survival of patients when adequate margins cannot be achieved.[Level of evidence: 3iiiDii] Unresectable or recurrent tumors may respond to chemotherapy.[21-23] Fast neutron-beam radiation therapy or accelerated hyperfractionated photon-beam schedules have been shown to be effective in the treatment of inoperable, unresectable, and recurrent tumors.[24-26]
Complications of surgical treatment for parotid neoplasms include facial nerve dysfunction and Frey syndrome also known as gustatory flushing and sweating and the auriculotemporal syndrome. Frey syndrome has been successfully treated with injections of botulinum toxin A.[27-29]References
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