Differences in Thyroid Cancer Incidence Increase in Eastern and Southern Croatia

Introduction: In most countries, the annual age-standardized incidence rate of thyroid cancer (TC) varies from 0.9-2.6 in men and 2.0- 5.9 in women per 100, 000. Aim: The aim of this study was to compare epidemiological characteristics of TC in eastern and southern Croatia, analyze possible differences and explain probable causes of increased incidence. Patients and methods: Epidemiological-clinical methods were used to analyze 1161 patient treated for TC (510 from eastern Croatia in the period between 1969 and 2005, and 651 from southern Croatia in the period from 1997 to 2006). Results: The average, age-standardized incidence rate of TC in the last ten years in eastern Croatia is 6.02 %000 and in southern Croatia 9.32 %000 (8.1 %000 in Croatia). Crude and age-standardized to the European and world population the incidence rates in both parts of Croatia show a trend of increase. The ratio papillary/follicular carcinoma is 3:1 in eastern Croatia, and in southern Croatia 6.4:1 (on islands and coastal area 7.8:1, in Zagora 4.2:1). Conclusion: Croatia is among counties with high incidence of TC, which is constantly increasing, and the incidence increase is mostly due to frequency rise of papillary carcinoma. Improved diagnosis of subclinical forms of TC is probably the main cause of increased incidence. Smaller representation of papillary carcinoma combined with higher iodine urine excretion in school children in eastern compared to southern Croatia, refutes the hypothesis of some authors of higher iodine intake as an etiological factor for papillary carcinoma incidence increase in former iodine- deficient areas.