It is generally thought that mixed tumors of the salivary glands sometimes undergo malignant change over a long period. Here, we report 6 cases of parotid tumor with suspected malignant transformation. The interval between the first evidence of tumor and histological verification ranged from 6 to 47 years. In one of the 6 cases the histological diagnosis was benign mixed tumor; this patient received irradiation therapy 9 years prior to malignant transformation. We consider that surgical treatment is better than long term observation or irradiation therapy even if benign tumor is suspected.
