Higher <scp>TSH</scp> level is a risk factor for differentiated thyroid cancer

<jats:title>Summary</jats:title><jats:sec><jats:title>Objectives</jats:title><jats:p>Higher thyroid‐stimulating hormone (<jats:styled-content style="fixed-case">TSH</jats:styled-content>) levels are associated with differentiated thyroid cancers (<jats:styled-content style="fixed-case">DTC</jats:styled-content>). To validate this association, we compared <jats:styled-content style="fixed-case">TSH</jats:styled-content> levels obtained from euthyroid patients with <jats:styled-content style="fixed-case">DTC</jats:styled-content> with <jats:styled-content style="fixed-case">TSH</jats:styled-content> levels from controls in the general population.</jats:p></jats:sec><jats:sec><jats:title>Design and patients</jats:title><jats:p>The case group included 1759 patients with <jats:styled-content style="fixed-case">DTC</jats:styled-content>, who underwent thyroid surgery at <jats:styled-content style="fixed-case">C</jats:styled-content>honnam <jats:styled-content style="fixed-case">N</jats:styled-content>ational <jats:styled-content style="fixed-case">U</jats:styled-content>niversity <jats:styled-content style="fixed-case">H</jats:styled-content>wasun <jats:styled-content style="fixed-case">H</jats:styled-content>ospital. The control group (<jats:italic>n</jats:italic> = 1548), who had participated in the Thyroid Disease Prevalence Study were used as a healthy control group. The subjects were divided into four groups of similar size according to their <jats:styled-content style="fixed-case">TSH</jats:styled-content> levels, with the first quartile used as a reference group.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The mean <jats:styled-content style="fixed-case">TSH</jats:styled-content> level of the case group was significantly higher than the mean <jats:styled-content style="fixed-case">TSH</jats:styled-content> level of the control group (1.95 ± 0.9 mIU/l <jats:italic>vs</jats:italic> 1.62 ± 0.8 mIU/l, <jats:italic>P</jats:italic> < 0.001), and was associated with <jats:styled-content style="fixed-case">DTC</jats:styled-content> risk. Multiple logistic regression, after controlling for age, gender and the presence of a family history of thyroid cancer, showed that the odds ratios and 95% confidence intervals for the second, third and fourth quartiles of <jats:styled-content style="fixed-case">TSH</jats:styled-content> levels were 1.27 (1.03–1.57), 1.55 (1.25–1.92) and 2.21 (1.78–2.74) respectively. No significant differences were observed in mean <jats:styled-content style="fixed-case">TSH</jats:styled-content> levels in patients with different tumour stages and tumour sizes.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>Having a high <jats:styled-content style="fixed-case">TSH</jats:styled-content> level within the normal range is an independent risk factor for <jats:styled-content style="fixed-case">DTC</jats:styled-content>, and may contribute to the initiation of thyroid carcinogenesis. <jats:styled-content style="fixed-case">TSH</jats:styled-content> levels in patients with thyroid nodules may be used as diagnostic adjuncts for the identification of high‐risk patients, who require further investigation and/or surgical intervention.</jats:p></jats:sec>