Different patterns of malignant change occur in pleomorphic adenoma, of which true malignant mixed tumor (carcinosarcoma) is one form. The other 2 forms are carcinoma ex pleomorphic adenoma and metastasizing benign pleomorphic adenoma.
By definition, carcinosarcoma is a biphasic malignant tumor with a carcinomatous component and a sarcomatous component. Most of these tumors arise in the background of pleomorphic adenoma; however, some arise de novo .
Carcinosarcoma of the salivary glands was first described by Kirklin et al in 1951.
The term true malignant mixed tumor in the salivary glands was first used by King in 1967 in a study that helped to renew interest in this tumor group.