Does life along the sea carry greater risk of thyroid cancer?

Aim of this study was to determine whether there are any differences between coastal and inland Dalmatia in incidence rates and clinical characteristics of thyroid cancer. Data on 651 persons who suffer from and have undergone surgery for thyroid cancer have been analysed. All patients lived in Dalmatia between 1997 and 2006. Data were collected via surveys, insight into medical histories and results of histopathological analysis. In Dalmatia, in the overall sample, there are no statistically significant differences in incidence between coastal and inland areas (chi2=3.03; df=1; p=0.082). Somewhat higher overall incidence has been recorded in the inland (8.5%000) than in the coastal Dalmatia (7.3%000). In the overall sample, in Dalmatia, women make up 81.4% of patients and papillary cancer accounts for 80.0% of all thyroid cancers. The ratio of papillary to folicullar cancer is 7.8:1 in coastal and 4.2:1 in inland Dalmatia. Papillary and medullary types are more common in the coastal area and follicular and anaplastic cancer types in the inland area and the differences are statistically significant (p>0.033). Epidemiological characteristics of thyroid cancer in coastal Dalmatia are in accordance with the characteristics of this cancer as described in iodine-sufficient areas: the most common type is papillary cancer, and the ratio of papillary to follicular is 7.8:1. Sex-wise, the coastal area records a higher ratio of male patients (1:3.8) than the inland area (1:7.1). There are no statistically significant differences in thyroid cancer incidence rates between coastal and inland Dalmatia. Epidemiological characteristics of thyroid cancer in inland Dalmatia are in some ways more similar to those of continental Croatia. This result could be the consequence of previous iodine insufficiency in inland Dalmatia.