Salivary Gland-Type Tumors of the Lung

Primary salivary gland-type tumors of the lung (SGTL) are rare and presumed to arise from the mucosal glands of the trachea and proximal bronchi. SGTLs are frequently mistaken for non-small cell carcinomas, but their incidence, clinical behavior, and prognosis are distinctly different from more aggressive forms of non-small cell lung neoplasms. The more common histologic subtypes of SGTLs include mucoepidermoid carcinoma (MEC) and adenoid cystic carcinoma (ACC). However, other neoplasms such as mixed tumor, epithelial–myoepithelial carcinoma (EM), acinic cell carcinoma (ACC), clear cell hyalinizing carcinoma (CCC), and oncocytoma have also been described. Together, SGTLs account for 0.1–0.2% of all thoracic malignancies. SGTLs have morphologic and immunohistochemical profiles similar to their counterparts of head and neck salivary gland origin. Thus, definitive diagnosis requires careful clinical, radiologic, and pathologic correlation. The incidence and behavior of salivary gland tumor subtypes vary with the tissue of origin, with most salivary gland tumors of lung origin being malignant, whereas tumors originating from the head and neck are frequently benign. Considerable variations in the clinical, epidemiologic, and histopathologic features of salivary gland tumor subtypes of lung origin also exist. Except for MEC, which may appear in adults and children, SGTLs are primarily adult tumors with a peak incidence in the fifth and sixth decades. Risk factors in the development of SGTL have not been clearly established, although an association with tobacco exposure for some phenotypes has been suggested. There is no specific staging system for SGTL. Data regarding prognosis is limited; however, histological type, grade, tumor size, and surgical resectability appear to be important prognosticators. Many questions regarding the optimal surgical approach and the efficacy of adjuvant chemotherapy and radiation therapy remain unanswered.