[Pleomorphic adenoma: pitfalls and clinicopathological forms of progression].

In the majority of cases the diagnosis of pleomorphic adenoma (PA) is straightforward. In "monomorphic" types of PA problems may result: Epithelial-rich PA need to be distinguished from basal cell adenoma or canalicular adenoma. PA dominated by mesenchymal, spindle-shaped differentiation need to be distinguished from myoepithelioma or soft tissue tumours like schwannoma. Focal biphasic-tubular differentiation with CK7/18-positive ductal cells is good evidence for a tumour within the wide spectrum of PA. Focal peripheral pseudoinfiltration can represent physiological growth pattern of PA; this may render a difficult distinction from low-malignant carcinomas like adenoid-cystic or epithelial-myoepithelial carcinoma, harbouring also tubular structures. The different progression steps of carcinoma ex pleomorphic adenoma (CEPA), starting with intraductal carcinoma, are highly relevant with respect to prognosis and therapy. Early stages including CEPA with minor extracapsular invasion show favourable prognosis, while cases with extensive extracapsular invasion carry a dismal prognosis.