Epidemiology and risk factors in thyroid carcinoma

Thyroid carcinoma represents less than 2% cancers although there is an increasing incidence, mainly of the papillary variety, due in part to improved diagnostic procedures. In contrast there is a remarkably higher prevalence of occult foci in detailed autopsy studies (up to 34%) suggesting the possibility of a spontaneous regression for most of them. Only 1-2% of latent tumours grow larger and become clinically important through environmental, genetic and cellular factors (two-mutational event model by Knudson). Each single histological subgroup has different influencing factors: X ray exposure, iodide diet intake, coexisting (autoimmune and non) thyroid disease such as thyroiditis, Graves' disease, goitre, dyshormonogenesis, heredity and altered cellular oncogenes have been considered. Of a series of 715 thyroid cancers operated on between 1967 and 1992 we analyze sex ratio, mean age, radiation exposure, coexisting thyroid disease, familial occurrence.