Association between thyroid cancer and cardiovascular disease risk: a nationwide observation study

Treatment with levothyroxine and radioiodine contribute alternative cardiovascular function in adults with thyroid cancer. The risks of long-term cardiovascular conditions among thyroid cancer patients is unknown. This study aimed to compare the incidence of coronary heart disease (CHD), ischemic stroke (IS), and atrial fibrillation (AF) among adults with thyroid cancer with that of the general population, especially when stratified by age (< 65 and ≥ 65 years old). This observational cohort study enrolled patients between January 1, 2011 and December 31, 2016 with a follow-up until December 31, 2018. This study analyzed the data of Taiwanese thyroid cancer patients registered on the National Taiwan Cancer Registry Database, with CHD and IS. SIR models were used to evaluate the association between thyroid cancer and CHD, IS, AF, and cardiovascular disease outcome, stratified by age and sex. SIR analyses were also conducted for both sexes, age groups (< 65, ≥ 65 years), and different follow-up years. After excluding 128 individuals (< 20 years or ≥ 85 years old) and with missing index data, 4274 eligible thyroid cancer patients without CHD history, 4343 patients without IS history, and 4247 patients without AF history were included for analysis. During the median follow-up of 3.5 (1.2) years among thyroid cancer patients, the observed number of new CHD events was 70; IS, 30; and AF, 20, respectively. The SIR was significantly higher for CHD (SIR, 1.57; 95% confidence interval [CI] 1.2-1.93) among thyroid cancer patients compared with the age- and sex-specific standardized population. However, the association between thyroid cancer and the risks of IS (SIR, 0.74; 95% CI 0.47-1), cardiovascular disease (SIR, 0.88; 95% CI 0.7-1.05), and atrial fibrillation (SIR, 0.74; 95% CI 0.42-1.06) were insignificant. Moreover, stratification by age < 65 or age ≥ 65 years old and by sex for CHD suggested that the diagnosis of thyroid cancer in the young may attenuate the CHD risk (SIR, 2.08; 95% CI 1.5-2.66), and the CVD risk was constant among both men (SIR, 1.63; 95% CI 1.03-2.24) and women (SIR, 1.53; 95% CI 1.06-1.99). The patients had persistent higher CHD risk for 5 years after cancer diagnosis. Thyroid cancer survivors have a substantial CHD risk, even at long-term follow-up, especially in those patients < 65 years old. Further research on the association between thyroid cancer and CHD risk is warranted.