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    Original Investigation
    Diabetes and Endocrinology
    July 23, 2020

    Association of Radioactive Iodine, Antithyroid Drug, and Surgical Treatments With Solid Cancer Mortality in Patients With Hyperthyroidism

    Author Affiliations
    • 1Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
    • 2Hirosoft International, Eureka, California
    • 3Department of Surgery, University of California, San Francisco
    JAMA Netw Open. 2020;3(7):e209660. doi:10.1001/jamanetworkopen.2020.9660
    Key Points español 中文 (chinese)

    Question  Are radioactive iodine or antithyroid drug treatments for hyperthyroidism associated with greater risk of solid cancer mortality compared with surgical management?

    Findings  In this cohort study of 31 363 patients who were cancer free at baseline, no association was found between treatment group (radioactive iodine, medications, and/or surgery) and risk of solid cancer mortality. Among patients receiving radioactive iodine treatment, the association with solid cancer mortality increased with greater total administered activity.

    Meaning  The findings suggest that the association between radioactive iodine treatment and solid cancer mortality is dose dependent.

    Abstract

    Importance  The long-term health effects of radioactive iodine (RAI) and antithyroid drug (ATD) treatments compared with surgery for hyperthyroidism remain uncertain.

    Objective  To compare solid cancer mortality rates associated with RAI and ATD treatments vs surgical management for hyperthyroidism.

    Design, Setting, and Participants  This multicenter cohort study assessed patients treated for hyperthyroidism from January 1, 1946, to December 31, 1964, with follow-up through December 31, 2014. Data analysis was performed from August 1, 2019, to April 23, 2020.

    Exposures  Management with RAI, ATDs, surgical intervention, or combinations of these treatments.

    Main Outcomes and Measures  Comparisons of solid cancer mortality rates in each treatment group with expected rates from the general population were assessed using standardized mortality ratios (SMRs), and internal comparisons were assessed using hazard ratios (HRs) adjusted for age, sex, and underlying diagnosis (Graves disease or toxic nodular goiter).

    Results  Of 31 363 patients (24 894 [79.4%] female; mean [SD] age, 46.9 [14.8] years) included in the study, 28 523 (90.9%) had Graves disease. The median follow-up time was 26.0 years (interquartile range, 12.3-41.9 years). Important differences in patient characteristics existed across treatment groups at study entry. Notably, the drug-only group (3.6% of the cohort) included a higher proportion of patients with prior cancers (7.3% vs 1.9%-4.0%), contributing to an elevated SMR for solid cancer mortality. After excluding prior cancers, solid cancer SMRs were not elevated in any of the treatment groups (SMR for surgery only, 0.82 [95% CI, 0.66-1.00]; SMR for drugs only, 0.90 [95% CI, 0.74-1.09]; SMR for drugs and surgery, 0.88 [95% CI, 0.84-0.94]; SMR for RAI only, 0.90 [95% CI, 0.84-0.96]; SMR for surgery and RAI, 0.66 [95% CI, 0.52-0.85]; SMR for drugs and RAI, 0.94 [95% CI, 0.89-1.00]; and SMR for drugs, surgery, and RAI, 0.85 [95% CI, 0.75-0.96]), and no significant HRs for solid cancer death were observed across treatment groups. Among RAI-treated patients, HRs for solid cancer mortality increased significantly across levels of total administered activity (1.08 per 370 MBq; 95% CI, 1.03-1.13 per 370 MBq); this association was stronger among patients treated with only RAI (HR, 1.19 per 370 MBq; 95% CI, 1.09-1.30 per 370 MBq).

    Conclusions and Relevance  After controlling for known sources of confounding, the study found no significant differences in the risk of solid cancer mortality by treatment group. However, among RAI-treated patients, a modest positive association was observed between total administered activity and solid cancer mortality, providing further evidence in support of a dose-dependent association between RAI and solid cancer mortality.

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