Most salivary gland tumors are benign and occur in the parotid glands. A painless salivary mass is the most common sign and is evaluated by fine-needle aspiration biopsy. Imaging with CT and MRI can be helpful. For malignant tumors, treatment is with excision and radiation. Long-term results are related to the grade of the cancer.
(See also Overview of Head and Neck Tumors.)
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SCOTT CAMAZINE/SCIENCE PHOTO LIBRARY
In general, the risk of malignancy is greater in smaller salivary glands than in larger salivary glands (eg, the parotid gland has a lower risk of malignancy than minor salivary glands) (1). 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.
Benign tumors
There are many types of benign salivary gland tumors. Pleomorphic adenomas (also known as mixed-type tumors) are the most common benign salivary gland tumors. Other benign tumors include papillary cystadenoma lymphomatosum (also known as Warthin tumors), oncocytomas, and adenomas.
Benign tumors with malignant potential
Pleomorphic adenomas (mixed-type tumors) can undergo malignant transformation, but this transformation usually occurs only after the benign tumor has been present for 15 to 20 years. Once malignant degeneration of a pleomorphic adenoma occurs, it is known as carcinoma ex pleomorphic adenoma. Carcinomatous elements in the tumor metastasize, making carcinoma ex pleomorphic adenoma a highly aggressive tumor with very low cure rates regardless of treatment.
Benign cylindromas (cutaneous adnexal tumors) can slowly undergo malignant transformation into adenoid cystic carcinomas, the most common malignant tumor of minor salivary glands (and of the trachea). The peak incidence of this malignant tumor is between ages 40 and 60 years, 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 common. Pulmonary metastases are common, although patients can live quite long with them.
Malignant salivary gland tumors
Other 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 (2), 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.
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.
General references
1. Guzzo M, Locati LD, Prott FJ, Gatta G, McGurk M, Licitra L. Major and minor salivary gland tumors. Crit Rev Oncol Hematol 2010;74(2):134-148. doi:10.1016/j.critrevonc.2009.10.004
2. Pinkston JA, Cole P. Incidence rates of salivary gland tumors: results from a population-based study. Otolaryngol Head Neck Surg 1999;120(6):834-840. doi:10.1016/S0194-5998(99)70323-2
Symptoms and Signs of Salivary Gland Tumors
Most benign and malignant salivary gland tumors manifest as a painless mass. However, malignant tumors may invade nerves, causing localized or regional pain, numbness, paresthesia, causalgia, or a loss of motor function.
Diagnosis of Salivary Gland Tumors
Fine-needle aspiration biopsy
CT and MRI for extent of disease
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 lungs, liver, bone, or brain is often indicated before treatment is selected.
Treatment of Salivary Gland Tumors
Surgery, sometimes plus radiation therapy
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 (1). While there is no data showing benefit from the addition of chemotherapy (in the absence of some identified genetic mutation) it is sometimes used with radiation for high grade tumors.
Treatment of mucoepidermoid carcinoma consists of wide excision and postoperative radiation for high-grade lesions. The 5-year survival rate is over 90% with the low-grade type, primarily affecting mucus cells, and less than 50% with the high-grade type, primarily affecting epidermoid cells (2). 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 favorable (3), cause-specific survival continues to decline up to 30 years after diagnosis due to a high rate of late distant metastasis, primarily to the lung (4).
The prognosis for acinic cell carcinoma is favorable after wide excision.
Primary treatment for carcinoma ex pleomorphic adenoma is parotidectomy with the goal of complete resection of all disease. A neck dissection is done if there is nodal disease and is considered for some patients without evidence of nodal spread.
All surgeries are designed to spare the facial nerve, which is sacrificed only in cases of direct tumor involvement with the nerve.
Treatment references
1. National Cancer Institute: Salivary Gland Cancer Treatment (PDQ®)–Health Professional Version. Updated August 2023.
2. Canadian Cancer Society: Salivary gland cancer. Prognosis and survival. Survival statistics for salivary gland cancer. Accessed July 30, 2024.
3. Ullah A, Ahmed A, Lee KT, Yasinzai AQK, Lewis JS Jr: Salivary gland adenoid cystic carcinoma in the U.S population: Importance of grade, site of metastases, and adjuvant radiation for survival. Am J Otolaryngol 2024;45(3):104266. doi:10.1016/j.amjoto.2024.104266
4. Lloyd S, Yu JB, Wilson LD, Decker RH: Determinants and patterns of survival in adenoid cystic carcinoma of the head and neck, including an analysis of adjuvant radiation therapy. Am J Clin Oncol 2011;34(1):76-81. doi:10.1097/COC.0b013e3181d26d45
Key Points
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.
Perform biopsy and CT and MRI if cancer is confirmed.
Treat using surgery, sometimes plus radiation therapy for certain cancers.
