Effects of radioactive iodine treatment on cardiovascular disease in thyroid cancer patients: a nationwide cohort study

Background: Radioactive iodine (RAI) treatment is a standard treatment in differentiated thyroid cancer (TC). However, its adverse effects on cardiovascular diseases (CVDs) have not been clearly elucidated.

Methods: In this retrospective cohort study based on the Korean National Health Insurance Service-National Health Screening Cohort (2002-2015), we analyzed 4,845 patients with TC with a median follow-up of 66 months. We evaluated and compared the risk of CVD between patients treated with and without RAI therapy. The primary CVD outcome was defined as a composite of ischemic stroke (IS), ischemic heart disease (IHD), hemorrhagic stroke (HS), or heart failure (HF).

Results: Overall, 2,533 patients (52.3%) received RAI treatment with a median cumulative dosage of 103 mCi [interquartile range (IQR), 40-162 mCi]. The incidence of the primary CVD outcome in patients who did not receive RAI therapy and those who did was 17.32 [95% confidence interval (CI), 15.07-19.90] and 13.96 (95% CI, 12.17-16.01) per 1,000 person-years, respectively, indicating an adjusted hazard ratio (HR) of 0.87 (95% CI, 0.71-1.07) after multivariate adjustments for variable confounding factors. The risks of IS (HR, 0.83; 95% CI, 0.51-1.34), IHD (HR, 0.90; 95% CI, 0.71-1.13), HS (HR 1.01; 95% CI, 0.49-2.09), and HF (HR 0.89; 95% CI, 0.49-1.63) were comparable between the patients who received RAI therapy and those who did not. There was no cumulative dose-dependent risk for CVD in TC patients who received RAI treatment.

Conclusions: RAI treatment is a prevalent and crucial treatment for TC, and has been used in more than half of TC patients in Korea from 2004 to 2015. This study found no significant between-group difference for the CVD risk in patients with TC who received RAI treatment and those who did not, giving further evidence to allay concerns related to the adverse effects of RAI.