Thyroid Cancer

Abstract

Thyroid cancer accounts for about 1% of all cancers. The incidence is higher in countries where goiter is endemic. This applies particularly to the less differentiated varieties of thyroid cancer. Age adjusted incidence rates (AAIR) are below 3 per 100,000 per year among males and almost two to three times higher for females, with little variation throughout the world. There are, however, some well-defined populations that show higher rates. For example, the female population of the Pacific Polynesian islands (AAIR 18.1 per 100,000 per year), the Filipino migrants to Hawaii (AAIR 6.1 for males and 18.2 for females) and to the US (AAIR 5.2 for males and 12.2 for females). High rates are also found in Iceland (AAIR 5.6 for males and 13.3 for females) and among Alaskan women. It is unfortunate that incidence data are not available by histological type because of the very different behavior of each type, suggesting also a different etiology. A second difficulty in the interpretation of statistics on thyroid cancer refers to the discrepancy between incidence data and autopsy data which seem to indicate a sex ratio of thyroid cancer around one (rather than 0.5–0.3), a stronger variability between countries, and a high prevalence of clinically occult disease.