The Geographical Pattern of Thyroid Cancer Mortality Between 1980 and 2009 in Italy

Background: Mortality for thyroid cancer (TC) is low and has been decreasing worldwide; yet few population studies based on mortality have been conducted. Several nonradiation risk factors have been associated with TC, including residence in goiter-endemic areas (as an indicator of iodine deficiency). We used mortality data to perform a spatial-temporal analysis regarding TC in Italy and investigated the association between mortality and socioeconomic status and geographical features (residing in a mountainous area is a proxy for iodine deficiency). Methods: We analyzed data from Italy's National Mortality Database (1980-2009). To evaluate temporal trends in mortality the age-standardized death rate (ASR) was used; to identify geographic areas with excess deaths due to TC standardized mortality rates (SMR) were calculated. We also calculated the rate ratios (RR) of the ASR and the 95% CI by sex. We performed a cluster analysis to identify municipalities with major departures from expected mortality, both in the entire study period and in two separate periods to evaluate the spatial-temporal variability. Finally, we evaluated the association between mortality and index of deprivation and altitude. Results: There were 16,473 deaths due to TC (10,690 females, 5783 males). The mean ASR was unsurprisingly low (0.58/100.000). There was a trend of decrease in mortality throughout Italy (-42% for 2007-2009 vs. 1980-1984), more pronounced among women. The decrease was greater in the north. Four geographic clusters were identified when considering the entire study period, two in the north and two in the south; however, the clusters in northern Italy refer to the earlier period (1980-1994) and those in southern Italy to the later period (1995-2009). Mortality was associated with residing in a mountainous area. A slight association with high socioeconomic status was found. Conclusions: This study reveals space-time differences in TC mortality in Italy. It shows an association between mortality and residing in mountainous areas, which is a proxy of iodine deficiency. The observed temporal north-south shift cannot be explained by socioeconomic differences, whereas the efficient prophylaxis program implemented in the 1980s in some areas of northern Italy can help to explain the disappearance of the clusters in those areas in the period 1995-2009.