An intracapsular carcinoma ex pleomorphic adenoma with lung metastases composed exclusively of benign elements: Histological evidence of a continuum between metastasizing pleomorphic adenoma and carcinoma ex pleomorphic adenoma

Malignant mixed tumors of the salivary glands, encompassing carcinoma ex pleomorphic adenoma (ca ex PA), carcinosarcoma and metastasizing pleomorphic adenoma (mPA), are rare neoplasms. Ca ex PA arises in a pre-existing pleomorphic adenoma (PA). When the malignant component does not breach the capsule of the parent PA, the lesion is termed intracapsular ca ex PA, a neoplasm which is thought to have no metastatic potential. Metastatic deposits of ca ex PA are composed exclusively of malignant elements or mixed benign and malignant components. We describe the case of a 62-year-old female with an intracapsular ca ex PA of the buccal mucosa with subsequent metastases to the lung. The metastatic deposits resembled benign PA with no histological evidence of malignancy. This pattern of spread is described with mPA, an entity that caused controversy in the past regarding its exact classification as a benign or malignant tumor. The possibility that ca ex PA originates from a mPA, with intracapsular ca ex PA representing an intermediate lesion in a histological continuum, is discussed.