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Benign Thyroid Diseases and Risk of Thyroid Cancer: A Nationwide Cohort Study

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Context: Thyroid nodules, adenomas, and goiter have consistently been associated with thyroid cancer risk. Few studies have assessed whether thyroid dysfunction and thyroid autoimmunity influence this risk.

Objective: To examine thyroid cancer risk after diagnoses of a wide range of benign thyroid conditions.

Design: Hospital and cancer registry linkage cohort study for the years 1978 to 2013.

Setting: Nationwide (Denmark).

Participants: Patients diagnosed with hyperthyroidism (n = 85,169), hypothyroidism (n = 63,143), thyroiditis (n = 12,532), nontoxic nodular goiter (n = 65,782), simple goiter (n = 11,582), other/unspecified goiter (n = 21,953), or adenoma (n = 6,481) among 8,258,807 residents of Denmark during the study period.

Main Outcome Measures: We computed standardized incidence ratios (SIRs) for differentiated thyroid cancer, excluding the first 12 months of follow-up after benign thyroid disease diagnosis.

Results: SIRs were significantly elevated for all benign thyroid diseases apart from hypothyroidism. SIRs were higher for men than women and in the earlier follow-up periods. Elevated SIRs were observed for localized and regional/distant thyroid cancer. After excluding the first 10 years of follow-up, hyperthyroidism [n = 27 thyroid cancer cases; SIR = 2.00; 95% confidence interval (CI): 1.32 to 2.92], nontoxic nodular goiter (n = 83; SIR = 4.91; 95% CI: 3.91 to 6.09), simple goiter (n = 8; SIR = 4.33; 95% CI: 1.87 to 8.53), other/unspecified goiter (n = 20; SIR = 3.94; 95% CI: 2.40 to 6.08), and adenoma (n = 9; SIR = 6.02; 95% CI: 2.76 to 11.5) remained positively associated with thyroid cancer risk.

Conclusions: We found an unexpected increased risk of differentiated thyroid cancer, including regional/distant disease, following diagnosis of hyperthyroidism and thyroiditis that could not be solely attributed to increased medical surveillance. Hypothyroidism was less clearly associated with thyroid cancer risk.

Original languageEnglish
JournalJournal of Clinical Endocrinology and Metabolism
Pages (from-to)2216-2224
Number of pages9
Publication statusPublished - 1 Jun 2018

    Research areas

  • Adult, Aged, Cohort Studies, Denmark/epidemiology, Female, Humans, Hyperthyroidism/complications, Hypothyroidism/complications, Incidence, Male, Middle Aged, Registries, Risk, Sex Factors, Thyroid Neoplasms/epidemiology, Thyroiditis/complications

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