Benign metastasizing pleomorphic adenoma of the parotid gland: A clinicopathologic puzzle

BACKGROUND: Pleomorphic adenoma constitutes the most common benign parotid gland tumor. Local recurrence after surgical treatment (lateral or total parotidectomy) has been described in 1% to 5% of cases. Malignant degeneration has been reported in 2% to 9% of cases of pleomorphic adenoma of salivary gland origin. Metastasizing pleomorphic adenomas without histologic evidence of malignancy have rarely been reported. Metastatic lesions have been discovered in bone, lymph nodes, the lung, oral cavity, pharynx, skin, liver, retroperitoneum, kidney, calvarium, and central nervous system. To the best of our knowledge, we hereby report the first case of pleomorphic adenoma of the parotid gland metastasizing to the ipsilateral maxilla. METHODS: We simultaneously examined apoptosis-related protein expression and markers of cell-proliferation activity in our case of benign pleomorphic adenoma metastasis and compared outcome with a control group of primary parotid pleomorphic adenomas. RESULTS: Analysis of p53, Bcl-2, MIB1, CD 105, p27, and p21 expression did not reveal significant differences between metastasizing pleomorphic adenoma of the salivary gland and the control group of primary parotid pleomorphic adenomas. CONCLUSIONS: Clinical rather than pathologic evidence seems to justify inclusion of metastasizing salivary pleomorphic adenoma in the group of low-grade malignant salivary tumors.