The new classification of Head and Neck Tumours (WHO) — any changes?

Abstract

The new classification of head and neck tumours was published in July 2005 (World Health Organization Classification of Tumours, Pathology and Genetics of Head and Neck Tumours; Leon Barnes, John W. Eveson, Peter Reichart, David Sidransky (Eds.), IARC Press, Lyon 2005). Few substantive changes relating to entities and classification were necessary in most of the eight chapters. In contrast, in Chapter 6, ‘‘Odontogenic Tumours’’, a number of important changes, including terminology, classification as benign or malignant or assignment to relevant subgroups in particular of benign tumours were made. Compared to the 1992 classification of odontogenic tumours, odontogenic cysts were not considered in the new classification with the result that the 1992 classification is still relevant for cysts of the jaws and maxillofacial region. Principally, in the new classification malignant tumours are dealt with before dealing with benign tumor entities. For odontogenic carcinomas a clarification of the metastasising ameloblastoma, which was inaccurately described in the 1992 classification, has now been achieved. Of importance is that the metastasizing ameloblastoma does so in spite of its benign histological features. In the presence of malignant histological features, the diagnosis of an ameloblastic carcinoma is made. The clear cell odontogenic carcinoma (CCOC), formerly clear cell odontogenic tumor, has now been added to the list of malignant odontogenic carcinomas. At the time of publication of the 1992 classification the number of published cases of CCOC was too small to provide a comprehensive picture. Publications at that time, however, did mention that the CCOC seemed to be more locally aggressive than ameloblastomas. Of particular importance is the fact that the new classification does not simply classify ameloblastoma as a single entity. Rather, it recognises the existence of variants, by using the plural term: ameloblastomas. Four ameloblastoma variants are now recognised: solid/multicystic ameloblastoma, extraosseous/peripheral ameloblastoma, desmoplastic ameloblastoma and unicystic ameloblastoma. The bioprofiles of these ameloblastomas vary in relation to age, distribution,