Salivary gland neoplasms are remarkable for their histologic diversity. These neoplasms include benign and malignant tumors of epithelial, mesenchymal, and lymphoid origin. Salivary gland tumors pose a particular challenge to the surgical pathologist. Differentiating benign from malignant tumors may be difficult, primarily because of the complexity of the classification and the rarity of several entities, which may exhibit a broad spectrum of morphologic diversity in individual lesions. In some cases, hybrid lesions may be seen. The key guiding principle to establish the malignant nature of a salivary gland tumor is the demonstration of an infiltrative margin.
The following cellular classification scheme draws heavily from a scheme published by the Armed Forces Institute of Pathology (AFIP). Malignant nonepithelial neoplasms are included in the scheme because these neoplasms comprise a significant proportion of salivary gland neoplasms seen in the clinical setting. For completeness, malignant secondary tumors are also included in the scheme.
The level of evidence required for informed decision making about genetic testing depends on the circumstances of testing. Evidence from a sample of high-risk families may be sufficient to provide useful information for testing decisions among people with similar family histories but is likely to be insufficient to make early recommendations for, or decisions about, testing in families with less dramatic histories or in the general population. Even among people with similar family histories, however,...
Where AFIP statistics regarding the incidence, or relative frequency, of particular histopathologies are cited, some bias may exist because of the AFIP methods of case accrual as a pathology reference service. When possible, other sources are cited for incidence data. Notwithstanding the AFIP data, the incidence of a particular histopathology has been found to vary considerably depending upon the study cited. This variability in reporting may be partially caused by the rare incidence of many salivary gland neoplasms.
The clinician should be aware that several benign epithelial salivary gland neoplasms have malignant counterparts, which are shown below:
Warthin tumor, also known as papillary cystadenoma lymphomatosum.
Basal cell adenoma (see basal cell adenocarcinoma).
Oncocytoma (see oncocytic carcinoma).
Sebaceous lymphadenoma (see sebaceous lymphadenocarcinoma).
Myoepithelioma (see myoepithelial carcinoma).
Cystadenoma (see cystadenocarcinoma).
Histologic grading of salivary gland carcinomas is important to determine the proper treatment approach, though it is not an independent indicator of the clinical course and must be considered in the context of the clinical stage. Clinical stage, particularly tumor size, may be the critical factor to determine the outcome of salivary gland cancer and may be more important than histologic grade. For example, stage I intermediate-grade or high-grade mucoepidermoid carcinomas can be successfully treated, whereas low-grade mucoepidermoid carcinomas that present as stage III disease may have a very aggressive clinical course.
Grading is used primarily for mucoepidermoid carcinomas, adenocarcinomas, not otherwise specified (NOS), adenoid cystic carcinomas, and squamous cell carcinomas.[1,3] Various other salivary gland carcinomas can also be categorized according to histologic grade as follows:[3,5,6,7,8]