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Thyroid cancer increases CVD morbidity risk
Adults treated for differentiated thyroid cancer have an increased risk for cardiovascular disease morbidity compared with those without cancer; and age, male sex and cardiovascular disease at the time of cancer diagnosis are predictors of morbidity, according to findings from researchers in Finland.
Nelli Pajamäki, MD, of the faculty of medicine and life sciences at the University of Tampere in Finland, and colleagues evaluated data from adults treated for differentiated thyroid cancer (DTC; n = 901) between 1981 and 2002 at two Finnish university hospitals and a randomly chosen reference group (n = 4,485) to compare long-term CV morbidity and mortality among them. They also sought to determine the effect of thyroid-stimulating hormone suppression and radioiodine treatment on CV outcomes. Median follow-up was 18.8 years for the DTC group and 19 years for controls.
Morbidity due to any CVD was greater in the DTC group compared with controls (HR = 1.16; 95% CI, 1.05-1.28), and more members of the DTC group were treated for CVD compared with controls during follow-up (53% vs. 48%). The DTC group had a higher risk for arrhythmias (HR = 1.16; 95% CI, 1.06-1.48) and atrial fibrillation (HR = 1.29; 95% CI, 1.06-1.57) than controls.
The risk for morbidity due to any CVD was increased in participants younger than 40 years (HR = 1.27; 95% CI, 1-1.6), those aged 40 to 59 years (HR = 1.23; 95% CI, 1.07-1.43) and those aged at least 60 years (HR = 1.17; 95% CI, 0.99-1.38) in the DTC group compared with the corresponding controls. Further, the risk for hospital treatment due to any CVD was higher for women in the DTC group compared with women in the control group (HR = 1.14; 95% CI, 1.02-1.28).
Overall mortality did not differ between the groups; however, CVD mortality was lower in the DTC group than controls (HR = 0.73; 95% CI, 0.58-0.92), which could be attributed to a lower mortality from coronary artery disease in the DTC group compared with controls (HR = 0.69; 95% CI, 0.5-0.95), according to researchers.
The risk for CVD morbidity was higher in the DTC group with geometric mean TSH level less than 0.1 mU/L (HR = 1.27; 95% CI, 1.03-1.58) and those treated with RAI ablation (HR = 1.18; 95% CI, 1.05-1.31) compared with the corresponding controls.
Age (HR = 1.04; 95% CI, 1.04-1.06), male sex (HR = 1.62; 95% CI, 1.19-2.22) and prevalent CVD at DTC diagnosis (HR = 1.68; 95% CI, 1.25-2.24) were predictors of morbidity due to any CVD in the DTC group.
“We found that the survival rate of patients diagnosed with DTC is excellent, but the risk of cardiovascular diseases is increased among patients treated for DTC, compared with age- and gender-matched controls,” the researchers wrote. “The increased risk is mostly accountable to an increased risk of atrial fibrillation. ... While the study raises concerns about the long-term cardiovascular effects of [thyroid hormone suppression therapy]-induced iatrogenic thyrotoxicosis, the optimal level of TSH remains to be settled in future studies.” – by Amber Cox
Disclosures: The authors report no relevant financial disclosures.
Perspective
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Patients with differentiated thyroid cancer are exposed to exogenous thyrotoxicosis as a treatment to decrease the frequency of thyroid cancer recurrence (Haugen BR, et al. Thyroid. 2016;doi:10.1089/thy.2015.0020). Whether this exogenous thyrotoxicosis is associated with cardiovascular morbidity and mortality is unclear. Pajamaki and colleagues conducted a retrospective study and found all arrhythmias (HR = 1.25, 95% CI 1.06-1.48) and atrial fibrillation (HR = 1.29, 95% CI 1.06-1.48) were more frequent in the DTC patients compared with the age- and sex-matched control group, with no difference in overall mortality between the two groups. Patients with a mean thyroid-stimulating level below 0.1 mU/L had increased arrhythmias compared with the corresponding controls. Although selection and attribution bias lowers our confidence in the results of the studies, this study adds to the body of evidence on the potential harm of exogenous hyperthyroidism (Biondi B, et al. Thyroid. 2010;doi:10.1089/thy.2009.0311). This study further validates the current guideline recommendations to risk stratify patients and treat more aggressively only in those with elevated risk for cancer recurrence or mortality.