[Histology of mucoepidermoid carcinoma. Analysis of 327 cases]

The mucoepidermoid carcinomas of the salivary glands (MEC) show histologically a wide spectrum of differentiation from solid epidermoid tumours to cystic mucous-filled tumours. Epidermoid cells, mucous cells and intermediate cells are the main cellular components. Besides clear cell (11.0%) and oncocytic (0.6%) variants and "cystic" (25.4%) tumours can be observed. According to the per cent of mucous cells and cystic spaces of the total tumour mass different degrees of histomorphologic differentiation can be distinguished. Therefore highly differentiated MEC (53.2%) with more than 50% mucous cells and cystic spaces, respectively low-differentiated MEC (46.8%) showing less than 50% mucous cells and cystic spaces can be subclassified. In respect of the therapeutic proceeding it should be recognized that the histopathological subclassification of MEC of the salivary glands (7) is based on morphological criteria only. It may not be equalized with a grading of malignancy since even highly differentiated MEC can grow infiltratively, sometimes osseo-destructively, to recur locally and to metastasize predominantly into the regional lymph nodes. Consequently the histopathological subclassification of MEC does not allow certain prognosis in individual cases.