Various treatments for hyperthyroidism were not found to be associated with “significant” differences in risk of death from solid cancers, according to the results of a large, multicenter cohort study published in JAMA Network.

The study included data on 31,363 patients with hyperthyroidism who were part of  the Cooperative Thyrotoxicosis Therapy Follow-up Study, which was a cohort study of patients who were treated for hyperthyroidism at US and UK medical centers between January 1, 1946, and December 31, 1964. Treatments included radioactive iodine, antithyroid drugs, surgery, or a combination of therapies. US patients were followed through December 31, 2014, translating to a median follow-up of 26 years.

Most patients — 71.3% — were treated with an antithyroid drug alone or in combination; radioactive iodine alone or in combination and surgery alone or in combination were used less frequently (62.5% and 43.6%, respectively). Baseline characteristics for each treatment group varied by age, underlying diagnosis, and comorbidities.

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The analysis initially showed that patients treated with antithyroid drug only appeared to have increased mortality rates for solid cancer (standardized mortality ratio [SMR]=1.31; 95% CI, 1.11-1.53), breast cancer (SMR=1.85; 95% CI, 1.31-2.62), and nonbreast solid cancer (SMR=1.22; 95% CI, 1.01-1.46). However, when patients with prior cancers were excluded from analysis, these risks were “attenuated.” The elevated risks were found to be restricted to the first 5 years of follow-up and disappeared when patients with prior cancers were excluded from the analysis.

In an adjusted analysis, the hazard ratio (HR) of solid cancer death did not differ by treatment when patients with prior cancers were excluded. The analysis did, however, reveal a “modest” positive association between risk of solid cancer death and total administered activity among patients treated with radioactive iodine (HR=1.08 per 370 MBq; 95% CI, 1.03-1.13; P =.001).

“After accounting for known sources of bias, we observed no significant differences in risk across treatment groups based on external and internal cohort comparisons,” the study authors concluded. “Notably, we found no evidence of an increased risk of solid cancer death associated with use of [antithyroid drugs].”

Disclosure: A study author declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Kitahara CM, Preston DL, Sosa JA, Berrington de Gonzalez A. Association of radioactive iodine, antithyroid drug, and surgical treatments with solid cancer mortality in patients with hyperthyroidism.  JAMA Netw Open. Published online July 23, 2020. doi:10.1001/jamanetworkopen.2020.9660