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Background:Anaplastic thyroid carcinoma (ATC) may arise de novoor from a preexistent differentiated carcinoma. It is well known that higher iodine intake in the diet causes higher frequency of papillary thyroid carcinoma, but decreases the frequency of follicular thyroid carcinoma. However, it is not known how the change in iodine intake influences the frequency of ATC. The aim of our study was to compare the incidence of ATC during the periods when the intake of potassium iodide in salt was 10 and 25 mg/kg.Methods:A total of 205 patients with ATC (140 women, 65 men; median, 69 years) were treated in the Republic of Slovenia between 1972 and 2008. In Slovenia, a country with a population of 2 million people, the salt was iodinated with 10 mg of potassium iodide/kg from 1972 to 1997. From 1998 to 2008 the degree of iodination of salt was increased to 25 mg of potassium iodide/kg. The frequency of ATC during the two periods and the characteristics of the patients during these periods were compared.Results:The mean incidences of ATC during 1972–1997 and 1998–2008 was 6.2 (range, 3–12) and 4 (range, 2–10) patients per year, respectively. During the period 1972–1997 and 1998–2008, the mean age of patients was 66.7 and 72.2 years (p= 0.02), and the mean tumor diameter was 9.6 and 8.6 cm (p= 0.21), respectively. However, the median survival of patients in both periods was 3 months.Conclusion:The incidence of ATC decreased after higher iodination of salt. The patients with ATC during the period of higher iodination of salt were older than those from the period with lower iodination of salt. [ABSTRACT FROM AUTHOR]