[Pleomorphic adenoma. Diagnostic difficulties. Value of ultrastructural and immunohistochemical studies. Apropos of 2 cases].

2 cases of pleomorphic adenoma with unusual histological feature are related. In the 1st case, the tumor was mistaken for a schwannoma. The electron microscopic study only permitted the diagnosis; in the 2nd case, the tumor, obviously malignant, was firstly diagnosed as synovial sarcoma; in this case also, ultrastructural study permitted to recognize a malignant mixed tumor with an unusual "sarcomatous" change of its myoepithelial component.