Salivary Gland Tumors
(See also Overview of Head and Neck Tumors.)
About 85% of salivary gland tumors occur in the parotid glands, followed by the submandibular and minor salivary glands, and about 1% occur in the sublingual glands. About 75 to 80% are benign, slow-growing, movable, painless, usually solitary nodules beneath normal skin or mucosa. Occasionally, when cystic, they are soft but most often they are firm.
The most common type is a pleomorphic adenoma (mixed tumor). Malignant transformation is possible, resulting in carcinoma ex pleomorphic adenoma, but this usually occurs only after the benign tumor has been present for 15 to 20 years. If malignant transformation occurs, the cure rates are very low, despite adequate surgery and adjuvant therapy.
Other benign tumors include monomorphic adenoma, oncocytoma, and papillary cystadenoma lymphomatosum (previously known as Warthin tumor). These tumors rarely recur and rarely become malignant.
Malignant tumors are less common and can be characterized by rapid growth or a sudden growth spurt. They are firm, nodular, and can be fixed to adjacent tissue, often with a poorly defined periphery. Eventually, the overlying skin or mucosa may become ulcerated or the adjacent tissues may become invaded.
Mucoepidermoid carcinoma is the most common salivary gland cancer, typically occurring in people in their 20s to 50s. It can manifest in any salivary gland, most commonly in the parotid gland but also in the submandibular gland or a minor salivary gland of the palate. Intermediate and high-grade mucoepidermoid carcinomas may metastasize to the regional lymphatics.
Adenoid cystic carcinoma is the most common malignant tumor of minor salivary glands (and of the trachea). It is a slowly growing malignant transformation of a much more common benign cylindroma. Its peak incidence is between ages 40 and 60, and symptoms include severe pain and, often, facial nerve paralysis. It has a propensity for perineural invasion and spread, with disease potentially extending many centimeters from the main tumor mass. Lymphatic spread is not a common feature of this tumor. Pulmonary metastases are common, although patients can live quite long with them.
Acinic cell carcinoma, a common parotid tumor, occurs in people in their 40s and 50s. This carcinoma has a more indolent course, as well as an incidence of multifocality.
Carcinoma ex mixed tumor is adenocarcinoma arising in a preexisting benign mixed tumor. Only the carcinomatous element metastasizes.
CT and MRI locate the tumor and describe its extent. Fine-needle aspiration biopsy of the mass confirms the cell type. A search for spread to regional nodes or distant metastases in the lung, liver, bone, or brain may be indicated before treatment is selected.
Treatment of benign tumors is surgery. The recurrence rate is high when excision is incomplete.
For malignant salivary gland tumors, surgery, sometimes followed by radiation therapy, is the treatment of choice for resectable disease. Currently, there is no effective chemotherapy for salivary cancer.
Treatment of mucoepidermoid carcinoma consists of wide excision and postoperative radiation for high-grade lesions. The 5-year survival rate is 95% with the low-grade type, primarily affecting mucus cells, and 50% with the high-grade type, primarily affecting epidermoid cells. Metastases to the regional lymphatics must be addressed with surgical resection and postoperative radiation therapy.
Treatment of adenoid cystic carcinoma is wide surgical excision, but local recurrence is common due to the propensity for perineural spread. Elective nodal treatment is less likely to be required because lymphatic spread is less common. Although the 5- and 10-year survival rates are quite good, the 15- and 20-year rates are worse with many patients developing distant metastases. Lung metastases and death are common, although many years (usually a decade or more) after the initial diagnosis and treatment.
The prognosis for acinic cell carcinoma is favorable after wide excision.
All surgeries are designed to spare the facial nerve, which is sacrificed only in cases of direct tumor involvement with the nerve.
Only about 20 to 25% of salivary gland tumors are malignant; the parotid gland is most commonly affected.
Cancers are firm, nodular, and can be fixed to adjacent tissue; pain and nerve involvement (causing numbness and/or weakness) are common.
Do biopsy and CT and MRI if cancer is confirmed.
Treat using surgery, sometimes plus radiation therapy for certain cancers.