The tumor is arising in a previously existed pleomorphic adenoma or theoretically it may start as a de novo malignant mixed tumor. This event is occurring in 5 -7 % of the mixed tumors, generally after having existed as such for more than 15 -20 years. The cells are malignant epithelial, myoepithelial cells admixed sometimes with malignant mesenchymal cells. The tumor is easily diagnosable on cytology in dedifferentiated and invasive cases: it consists mostly of malignant squamous, in some cases keratinizing squamous cells, atypical glandular cells. Mucoepidermoid cancer, small cell tumor may also develop in malignant mixed tumors. Mitotic figures may be present. There is a rare variant of in situ malignant mixed tumor: in these cases the same kinds of malignant myoepithelial or epithelial cells are present, they invade the capsule and vessels inside the lesion, but are not invasive towards the surrounding salivary gland tissue. Recently a new entity was described called sclerosing clear cell myoepithelial carcinoma, which is characterized by a specific molecular change ( EWSR1 rearrangement). This tumor also develops in preexisting mixed tumors. No cytology publication on this latter tumor until now.
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