Thyroid cancer is a relatively rare form of cancer, causing less than one per cent of cancer deaths, but with higher incidence in younger women, and, together with gallbladder cancer, it is one of the non sex-related site cancers whose rates are higher for females than for males. [1] [2] [3] An established risk factor for thyroid cancer is a history of benign thyroid disease, mostly goitre, adenomas and hyperthyroidism. 4-9 Other recognized risk factors include exposure to radiotherapy 2 and

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... ioactive iodine, 10-12 mainly during childhood, 13-15 and long-term residence in regions with iodine imbalances, including high endemic goitre areas, 9 such as iodine-deficient regions in the Alps, or areas with high iodine levels, like Iceland and Hawaii. [16] [17] [18] [19] Furthermore, a diet poor in vegetables and fruit 20-23 and rich in starchy food, 24 which are indicators of a poor diet in several populations, has been associated with an increased risk of thyroid cancer. 6, 7, 25 Between 1986 and 1992 we conducted a case-control study of thyroid cancer in Italy, whose results confirmed the strong association with history of benign thyroid disease. 9 Other determinants for thyroid cancer risk were a history of radiotherapy, long-term residence in endemic goitre areas 9 and selected aspects of diet. 24 The role of each of these factors, or their combination, depends not only on the strength of the association, but also on the prevalence of each factor in the population. To address these issues, we estimated the population attributable risk (PAR) of thyroid cancer, i.e. the proportion of thyroid cancer cases in Conclusions Exposure to a few simply identified and potentially modifiable risk factors or indicators (benign thyroid disease, residence in endemic goitre area and a poor diet) explained about 60% of thyroid cancer cases in this Italian population, indicating the theoretical scope for prevention.