Pleomorphic adenoma is the most common salivary gland tumor, and the histologic pattern of this tumor is one of its most characteristic features. Cyst formation in this tumor is sometimes observed, however, the etiology of which is unknown. In this paper, two cases of pleomorphic adenoma with a large cyst were examined light microscopically, and the etiology of cyst formation in the tumor was discussed. Case 1 was a 80-year-old woman with tumor in the left hard palate. The large cyst which is lined by keratinized squamous epithelia was observed in the central portion of the tumor.
Case 2 was a 48-year-old man with tumor in the right parotid gland. The large cyst in which its wall was a lining of compressed fibrous connective tissue, was also observed in the tumor.
