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FROM THE EXPERT: Focus on Salivary Glands
Cancers of the Salivary Glands Salivary gland cancers are a diverse and rare group of neoplasms. They have an overall incidence of approximately 2.5 to 3.0 cases per 100,000 per year. Malignant salivary gland cancers comprise approximately 0.5% of all malignancies and 3% to 5% of all cancers arising in the head and neck region. They typically present in patients who are in the sixth or seventh decade of life. The cause of most salivary gland cancers is unknown, however, several occupations are associated with an increased risk for these cancers, including plumbing, asbestos mining, rubber products manufacturing, and some types of woodworking.
Anatomically, salivary glands are composed of major and minor glands, and tumors can develop in either group. The major glands consist of the parotid, submandibular, and sublingual glands, and the minor glands are comprised of the oral mucosa, palate, uvula, floor of mouth, posterior tongue, retromolar area and peritonsillar area, pharynx, larynx, and paranasal sinuses. 70% to 80% of all salivary gland neoplasms originate in the parotid gland whereas the palate is the most common site of minor salivary gland tumors.
More than 50% of salivary gland tumors are benign. 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. The most common benign major and minor salivary gland tumor histologically is the pleomorphic adenoma. This benign tumor comprises about 50% of all salivary gland tumors and 65% of parotid gland tumors. The most common malignant tumor of both the major and minor salivary glands is the mucoepidermoid carcinoma, accounting for approximately 10% of all salivary gland neoplasms and 35% of malignant salivary gland neoplasms. It occurs most often in the parotid gland.
Presentation of benign tumors of both the major or minor salivary glands present is most commonly painless swelling. This usually occurs in the parotid, submandibular, or the sublingual glands. For malignant tumors there may also be neurological signs, such as numbness or weakness, which is caused by involvement of a nerve. Approximately 10% to 15% of malignant parotid neoplasms present with pain, and facial pain that is persistent is highly suggestive of malignancy. The majority of parotid tumors, both benign and malignant, present as a mass in the gland without any symptoms.
Treatment-wise, early-stage low-grade malignant salivary gland tumors are usually curable by adequate surgical resection alone. When the tumor occurs in a major salivary gland, the prognosis is more favorable. Tumors of the parotid gland are most favorable, followed by those in the submandibular gland. The least favorable primary sites are the sublingual and minor salivary glands. Large bulky tumors or high-grade tumors often carry a poorer prognosis. These may best be treated by surgical resection combined with postoperative (adjuvant) radiation therapy. Other prognostic factors include the clinical stage, tumor size, grade, histology, site of origin, nerve involvement, lymph node involvement, fixation to skin or deep structures, and whether there is spread to distant sites.
If perineural invasion is seen postoperatively, particularly in high-grade adenoid cystic carcinomas, it should be specifically identified and treated. Radiation therapy may also increase the chance of local control and increase the survival of patients when adequate margins cannot be achieved. Unresectable or recurrent tumors may respond to chemotherapy. For inoperable, unresectable, and recurrent tumors, a faster course of radiation therapy with a higher dose per fraction (accelerated hypofractionation) has been shown to be effective as a form of treatment.
Dr. Leonard Farber is a A Board Certified physician in Radiation Oncology, and the founder of The Farber Center for Radiation Oncology
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