RESUMO
Cancer of the thyroid accounts for less than 1% of all cancers recognised each year, but the incidence is rising. Much of the early work of the epidemiology and aetiology of thyroid cancer was based on the assumption that thyroid cancer can be treated as an entity. The recognition that two distinct types of endocrine cell occur within the thyroid has made it clear that any discussion of the aetiology and epidemiology of thyroid malignancies must take into account the histological classification of these tumours. Moreover, there are difficult problems to be considered when comparing thyroid cancer incidence across tumour registries, because of a lack of standardisation or morbidity data collection, difficulties in histological diagnosis, varying rates of diagnosis of occult papillary carcinoma, and prevalence and techniques of autopsies. So far only a relatively small proportion of thyroid cancer cases can be explained with adequate certainty as regards epidemiology and aetiology. As in cancer in general, the aetiology and epidemiology of thyroid cancer in detail remains unknown in the majority of cases.