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Abstract
Objective To evaluate whether hyperthyroidism or hypothyroidism increases the risk of subsequent breast cancer in an Asian population.
Design Nationwide population-based case–control study.
Setting All healthcare facilities in Taiwan.
Participants A total of 103 466 women (mean age 53.3 years) were enrolled.
Methods 51 733 adult women with newly diagnosed primary breast cancer without a previous cancer history between 2006 and 2011 were identified and included in our study. 51 733 women with no cancer diagnosis prior to the index date were age matched as controls. Diagnosis of hyperthyroidism or hypothyroidism prior to the diagnosis of breast cancer or the same index date was identified, age, histories of thyroid disease treatment, oestrogen use and radioactive iodine treatment were adjusted.
Main outcome measures To identify risk differences in developing breast cancer among patients with a medical history of hyperthyroidism or hypothyroidism.
Results There was a significantly increased risk of breast cancer in women with hyperthyroidism under the age of 55 years (age <45: OR 1.16, P=0.049; age 45–55: OR 1.15, P=0.019). Patients with hypothyroidism also showed an increased risk of breast cancer (OR 1.19, P=0.029) without statistical significance after stratification by age group (age <45, 45–55, >55 years). Treatment for thyroid disorders did not alter the association in subgroup analyses (P=0.857; 0.262, respectively).
Conclusions Asian women under 55 years of age with history of hyperthyroidism have a significantly increased risk of breast cancer regardless of treatment. Women with history of hypothyroidism may also have an increased risk.
- thyroid disease
- epidemiology
- breast tumours
- preventive medicine
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Footnotes
Contributors Concept of study: C-HW and T-HL. Study design: C-HW, XL, C-HL and T-HL. Statistical analysis: Y-HC and C-HL. Interpretation of results: C-HW, Y-HC, XL and C-HL. Manuscript writing: C-HW. The other authors provided inputs, expertise and critical review of the manuscript. C-HW and T-HL contributed as co-senior authors to this article.
Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Disclaimer The interpretation and conclusions contained herein do not represent those of National Health Insurance Administration, Department of Health or National Health Research Institutes.
Competing interests None declared.
Patient consent Not required.
Ethics approval This study has been approved by the Institutional Review Board of Taichung Veterans General Hospital, Taichung, Taiwan (IRB no: CE13151B-3). The study is based in part on data from the National Health Insurance Research Database provided by the Bureau of National Health Insurance, Department of Health and managed by National Health Research Institutes.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Extra data are available by emailing the corresponding author (jth.lin@gmail.com).
Presented at The preliminary results from this study have been presented in part at the 86th Annual Meeting of the American Thyroid Association in Denver, Colorado, USA, by C-HW, 21–25 September 2016.