Malignant salivary gland neoplasms represent 3–4% of head and neck malignancies and <0.5% of all cancers diagnosed yearly in the United States, with an incidence of only 1–2 per 100,000 individuals. Unlike the more common mucosal head and neck cancers, which, in general, are attributed to excessive tobacco and alcohol use, specific carcinogenic factors for malignant salivary gland growths have not been as clearly identified. Viral infections, radiation, environmental exposure, and genetic factors have been hypothesized as causes. Malignant salivary gland tumors are classified by the World Health Organization as carcinomas, nonepithelial tumors, lymphomas, metastatic or secondary tumors, and unclassified tumors (Table 19–1).
Table 19–1. World Health Organization Classification of Salivary Gland Malignant Neoplasms. |Favorite Table|Download (.pdf)
Table 19–1. World Health Organization Classification of Salivary Gland Malignant Neoplasms.
- Mucoepidermoid carcinoma
- Adenoid cystic carcinoma
- Acinic cell carcinoma
- Malignant mixed tumor
- Carcinoma in pleomorphic adenoma
- Polymorphous low-grade adenocarcinoma (terminal duct adenocarcinoma)
- Epithelial-myoepithelial carcinoma
- Salivary duct carcinoma
- Basal cell carcinoma
- Mucinous adenocarcinoma
- Papillary cystadenocarcinoma
- Adenocarcinoma, not otherwise specified (NOS)
- Clear cell carcinoma
- Sebaceous carcinoma and lymphadenocarcinoma
- Oncocytic carcinoma
- Malignant myoepithelioma (myoepithelial carcinoma)
- Squamous cell carcinoma
- Adenosquamous carcinoma
- Lymphoepithelial carcinoma
- Small cell carcinoma
- Undifferentiated carcinoma
- Other carcinomas
- Squamous cell carcinoma
- Renal cell carcinoma
- Thyroid carcinoma
Only 20–25% of parotid gland neoplasms, approximately 45–50% of submandibular gland neoplasms, and > 70% of sublingual and minor salivary gland neoplasms are malignant. However, because 75–80% of salivary gland neoplasms are located in the parotid gland, this gland is still the most common salivary gland to be affected with a malignant neoplasm; a ratio of 40:10:1 is cited for malignant tumors of the parotid, submandibular, and sublingual glands, respectively.
Table 19–2 shows the histologic types of malignant salivary gland disease in order of frequency. The disease site also is important for predicting the histology. Mucoepidermoid carcinoma is most common in the parotid gland. Approximately half of malignant submandibular gland neoplasms are adenoid cystic carcinomas. Minor salivary gland malignant neoplasms are most often adenoid cystic carcinomas and adenocarcinomas. Prognosis varies according to histologic type, stage, and primary site.
Table 19–2. Frequency of Salivary Gland Malignant Neoplasm by Histologic Type. |Favorite Table|Download (.pdf)
Table 19–2. Frequency of Salivary Gland Malignant Neoplasm by Histologic Type.
|Histologic Type||Frequency of Occurrence (%)|
|Adenoid cystic carcinoma||22|
|Malignant mixed tumor||13|
|Acinic cell carcinoma||7|
|Squamous cell carcinoma||4|
The salivary gland unit is depicted in Figure 19–1. The acinus is located at the distal end of a salivary unit. It consists of pyramidal saliva-forming cells arranged around a central lumen, with myoepithelial cells interposed between the basal side of these cells and the basement membrane. Acinar cells may be serous, mucinous, or seromucinous, which explains the different chemical compositions of the saliva of each gland.
The salivary gland unit. (Adapted, with permission, from Thawley SE, Panje WR, Batsakis JG, Lindberg RD. Comprehensive Management of Head ...