During the past several decades, an increasing incidence of thyroid cancer has been reported in many parts of the world. To date, no study has compared trends in thyroid cancer incidence across continents. We examined incidence data from Cancer Incidence in Five Continents (CI5) over the 30-year period 1973-2002 from 19 populations in the Americas, Asia, Europe and Oceania. Thyroid cancer rates have increased from 1973-1977 to 1998-2002 for most of the populations except for Sweden, in which the incidence rates decreased about 18% for both males and females. The average increase was 48.0% among males and 66.7% among females. More recently, the age-adjusted international thyroid cancer incidence rates from 1998-2002 varied 5-fold by geographic region for males and nearly 10-fold for females by geographic region. Considerable variation in thyroid cancer incidence was present for every continent but Africa, in which the incidence rates were generally low. Our analysis of published CI5 data suggests that thyroid cancer rates increased between 1973 and 2002 in most populations worldwide and that the increase does not appear to be restricted to a particular region of the world or by the underlying rates of thyroid cancer.

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Increasing evidence has suggested that microRNAs (miRNA) play an important role in tumorigenesis. As transcriptional regulators, altered miRNA expression may affect many cancerrelated biological pathways, indicating that miRNAs can function as tumor suppressors and/or oncogenes. We first performed a genetic association analysis by screening genetic variants in 15 miRNA genes and detected that a common sequence variant in hsa-miR-196a-2 (rs11614913, C!T) was significantly associated with decreased breast cancer risk ( for homozygous variant: odds ratio, 0.44; 95% confidence interval, 0.28-0.70). Hypermethylation of a CpG island upstream (-700 bp) of the miR-196a-2 precursor was also associated with reduced breast cancer risk (odds ratio, 0.35; 95% confidence interval, 0.15-0.81).

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