Survival of the Fittest: Thyroid Cancer Survivors and Cardiovascular Disease Risks

A study published in The Journal of Clinical Endocrinology & Metabolism demonstrates a number of risks between thyroid cancer and cardiovascular disease. While the research shows typical co-morbidities in certain populations, could there be an actual link between the two?

With advances in cancer management and treatment, patients with cancer diagnoses are living longer. However, that very treatment may carry its own proprietary risks. “Cancer survivors are living longer today and need to be aware of long-term disease risks of certain diseases that can be a result of their cancer treatment and lifestyle factors,” says Jihye Park, PhD candidate in the Department of Epidemiology at UNC Gillings School of Global Public Health in Chapel Hill, N.C. For thyroid cancer survivors, in particular, who tend to be young adults with very high five-year survival rates at 98.1%, does survival expose patients to additional disease risk? What is their quality of life, given their near-normal life expectancy?

Who’s at Risk?

In “Risk Factors for Cardiovascular Disease Among Thyroid Cancer Survivors: Findings from the Utah Cancer Survivors Study,” published in The Journal of Clinical Endocrinology & Metabolism, lead author Park and team set out to answer these very questions. With thyroid cancer incidence on the rise in the U.S., it is expected to become the fourth most common cancer here in just a dozen or so years, rapidly outranking its current status as the eighth most common cancer, with 64,300 new cases diagnosed in 2016. However, some states have higher rates than others, possibly — but not definitively — due to environmental exposures. Utah has the third highest incidence rate of thyroid cancer at 19.03 per 100,000 population and was the location of the research team’s study cohort. Using the Utah Cancer Registry coupled with demographic and clinical data from electronic medical records (EMRs) (e.g., sex, birth year, age at thyroid cancer diagnosis, race/ethnicity, body mass index [BMI], year of cancer diagnosis, cancer stage, cancer histologic type, number of cancers, cancer treatment) and Utah Department of Health vital records, the team was able to find primary thyroid cancer cases diagnosed from 1997 to 2012 and link them with treatment data as well as assign a Charlson comorbidity index (CCI) score to establish baseline health before the thyroid cancer was diagnosed.

“In the United States, there are more than 800,000 thyroid cancer survivors today. With more thyroid cancer patients surviving for longer periods, it is important to know which thyroid cancer survivors are at higher risk of developing life-threatening conditions such as CVD.” – Jihye Park, PhD candidate, Department of Epidemiology, UNC Gillings School of Global Public Health, Chapel Hill, N.C.

The team reasoned that the thyroid cancer treatments that commonly accompany thyroidectomy might be correlated with long-term adverse health outcomes, with nearly half of patients with thyroid cancer receiving radioactive iodine (RAI) to prevent recurrence. Additionally, in some cases, thyroid-stimulating hormone (TSH) suppression may be done. Both adjunctive treatments have been suggested to increase risk of cardiovascular disease (CVD). So, the team set out to elucidate the connections between potential risk factors (both clinical and demographic), treatment effects, and CVD outcomes in thyroid cancer survivors. “In the United States, there are more than 800,000 thyroid cancer survivors today,” Park explains. “With more thyroid cancer patients surviving for longer periods, it is important to know which thyroid cancer survivors are at higher risk of developing life-threatening conditions such as CVD.”

Saving Their Necks

The study cohort comprised 3,822 thyroid cancer survivors, most of whom (almost 92%) had a diagnosis of papillary carcinoma. They were predominantly white (96.1%) and female (78.8%). More than half of them underwent postoperative adjuvant RAI treatment in addition to surgery. Almost half of them (1,719; 45.0%) developed at least one cardiac or vascular disease one to five years after their cancer diagnosis.

“We studied potential risk factors, treatment effects, and cardiovascular CVD outcomes among nearly 4,000 thyroid cancer survivors over a 15-year period using the statewide Utah Population Database, and we identified who are at high risk of developing CVD after their primary thyroid cancer diagnosis,” Park says. “We found that male thyroid cancer survivors have an almost 50% higher risk of developing CVD versus female, and obese thyroid cancer survivors have a 41% increased risk. TSH suppression therapy was also associated with a 25% increased risk of CVD. Patients who received radiation therapy following surgery also had a higher risk of developing cerebrovascular disease compared to patients who received surgery only.” The latter risk is possibly because of the proximity of the carotid arteries to the thyroid gland in the neck. Thus, the role and dosage of RAI after thyroid surgery, a treatment strategy that grew more common over the study period, needs to be fully examined to assess the risk of developing life- and quality-of-life–threatening circulatory system disorders.

“Our research findings provide important clinical implications for future interventions for better outcomes among thyroid cancer survivors,” says Park. Their findings are supported by their large sample size as well as by the use of EMR data rather than patient self-report as previous studies have done. Related knowledge gaps that still need to be filled include specifics about types of TSH suppression therapy and the RAI treatment, dose, and frequency used to clarify what treatment has what long-term effect. An evaluation of lifestyle choices like diet and level of physical activity also needs to be factored in to see what role, if any, these potential cofounders might play. Finally, a more diverse cohort should be studied to investigate potential race/ethnicity-related differences in outcomes.

In the meantime, according to Park and team, there are clear implications for both patients and clinicians. “We hope our results help them acknowledge potential risk factors for CVD,” she says. “We hope cancer survivors who are at higher risk can be continuously monitored and screened for CVD for both earlier detection and preventative care.”

-Horvath is a freelance writer based in Baltimore, Md. She wrote about prenatal thyroid screening in the January issue.


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