title: Hyperthyroidism and thyroid cancer risk: a population-based cohort study.
abstract: OBJECTIVE
  Thyroid hormones regulate the rate of metabolism and affect the differentiation and growth of many tissues in the body. We investigated the association between hyperthyroidism and cancer risk in Taiwan.
  
  
  METHODS
  A random sample of 1 000 000 individuals from Taiwan's National Health Insurance database was enrolled. We found 17 033 patients to have newly diagnosed hyperthyroidism between 2000 and 2005. These patients were recruited along with a match cohort of 34 066 patients without hyperthyroidism. Starting from index date, we followed up all patients for 4 years to identify those who developed cancer.
  
  
  RESULTS
  During the 4-year follow-up study, cancer was diagnosed in 1.23% of patients with hyperthyroidism and 1.02% of the member of the comparison cohort. Regression analysis showed that patients with hyperthyroidism were at greater risk of cancer incidence, especially thyroid cancer, compared the comparison cohort (HR: 1.213; 95% CI: 1.022-1.440; p<0.05 and HR: 7.355; 95% CI: 3.885-13.92; p<0.05, respectively). After adjusting for age, gender, diabetes mellitus, hypertension, hyperlipidemia, gout, geographic region, and income, patients with hyperthyroidism remained at increased risk of cancer incidence and thyroid cancer (Adjusted HR: 1.206; 95% CI: 1.015-1.433 and 6.803; 95% CI: 3.584-12.91, respectively) (both p<0.05). The longer the duration of hyperthyroidism, the greater the risk of thyroid cancer.
  
  
  CONCLUSIONS
  This 4-year follow up study suggests that patients with hyperthyroidism are at increased risk of cancer, especially thyroid cancer.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine, Chi Mei Medical Center, Tainan, Taiwan.
authors.forename: N-C
authors.initials: NC
authors.lastname: Yeh
authors.forename: C-W
authors.initials: CW
authors.lastname: Chou
authors.forename: S-F
authors.initials: SF
authors.lastname: Weng
authors.forename: C-Y
authors.initials: CY
authors.lastname: Yang
authors.forename: F-C
authors.initials: FC
authors.lastname: Yen
authors.forename: S-Y
authors.initials: SY
authors.lastname: Lee
authors.forename: J-J
authors.initials: JJ
authors.lastname: Wang
authors.forename: K-J
authors.initials: KJ
authors.lastname: Tien
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006980:Hyperthyroidism / Q000150:complications* / Q000453:epidemiology* / Q000473:pathology; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D013624:Taiwan / Q000453:epidemiology; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000473:pathology; D013997:Time Factors