Adenoid cystic carcinoma arising in a pleomorphic adenoma of the parotid gland. An aspiration cytology and ultrastructural study.

The unusual occurrence of an adenoid cystic carcinoma arising in a pleomorphic adenoma is described, with emphasis on the cytomorphology of the neoplasm in a fine needle aspiration specimen. The ultrastructural findings are detailed, including the acellular hyaline spheres so characteristic of this tumor.