Long-term cardiovascular morbidity and mortality in patients treated for differentiated thyroid cancer

SummaryObjectives Thyroid hormone suppression therapy has been widely used in the treatment of thyroid cancer, but concerns have been raised about the cardiovascular risks of this treatment. The objective of this study was to evaluate long-term cardiovascular morbidity and mortality in patients treated for differentiated thyroid cancer (DTC) and to assess the effect of TSH suppression and radioiodine (RAI) treatment on the cardiovascular outcome. Design Retrospective cohort study. Patients and measurements Patients (n = 901) treated for DTC between 1981 and 2002 at 2 Finnish University hospitals were compared with a randomly chosen reference group (n = 4485) matched for age, gender and the place of residence. Kaplan-Meier and Cox regression analyses were used to estimate the risk of morbidity or death due to different cardiovascular diseases (CVD) after the diagnosis of DTC. Results Morbidity due to any CVD (hazard ratio [HR] 1.16, 95% confidence interval [CI] 1.05-1.28) and due to all arrhythmias (HR 1.25, CI 1.06-1.48) and atrial fibrillation (AF) (HR 1.29, CI 1.06-1.57) was more frequent in the DTC patients than in the controls. The increased cardiovascular morbidity was confined to patients with a mean TSH level below 0.1 mU/L (HR 1.27, CI 1.03-1.58) and to those treated with RAI (HR 1.18, CI 1.05-1.31). Cardiovascular mortality, however, was lower among the patients than the controls (HR 0.73, CI 0.58-0.92), due to a lower mortality from coronary artery disease. Conclusions Differentiated thyroid cancer patients have an increased CVD morbidity, which is mostly accountable to AF and to TSH suppression below 0.1 mU/L.