In the United States, one of the most common treatments for hyperthyroidism is radioactive iodine (also known as RAI). Now, new research is raising the possibility that hyperthyroid patients face an increased risk of cancer in other parts of the body after RAI treatment. If you are hyperthyroid, this probably sounds like a lose-lose situation. But before you run to your doc to overhaul your treatment plan, keep reading. We've got answers to seven questions we bet you’re wondering about.
What is Hyperthyroidism Anyway?
Hyperthyroidism is a condition that makes your thyroid gland overactive. As your metabolism speeds up in response to excess thyroid hormone, you may experience symptoms such as weight loss, anxiety, diarrhea, high blood pressure, and fatigue. In the U.S., the prevalence of hyperthyroidism is 1.2%, according to the American Thyroid Association. The autoimmune condition Graves' disease triggers most cases.
How Does RAI Treat Hyperthyroidism?
RAI is a radioactive isotope of iodine, orally administered as a pill or liquid. Once taken, the radiation is absorbed primarily by the thyroid gland, where it destroys cells and the gland’s ability to produce the thyroid hormone. RAI has been one of the primary treatments for hyperthyroidism in the U.S. since the 1940s; it's also frequently used at higher doses to treat thyroid cancer.
RAI is considered a safe and effective therapy, as it's non-invasive and usually permanent. The primary concern about the treatment is that other organs absorb some radiation.
What Do We Know About Cancer After RAI?
Previous research has demonstrated that thyroid cancer patients–who frequently have high-dose RAI treatment after thyroid surgery–may face an increased risk of secondary cancers. The risks include bone and soft-tissue sarcomas, salivary gland and digestive-tract cancers, and leukemia.
But a new study, funded by the National Cancer Institute (NCI) and published in the journal JAMA Internal Medicine, had even more sobering news. Scientists found that patients might face an increased risk of death from other cancers after RAI for hyperthyroidism.
What Did the NCI Study Report?
The researchers identified 18,805 patients with hyperthyroidism who were treated with RAI. In the study group, 78% were women, and almost all had hyperthyroidism as a result of Graves’ disease. These patients had no history of cancer at the time of their first RAI treatment.
According to the NCI study, RAI for hyperthyroidism increased the risk of death from all solid tumors 6% for every 100 milligray (mGy) dose; this included cancers of the breast, mouth, thyroid, esophagus, stomach, colon, rectum, liver, pancreas, lung, bladder, kidney, brain, uterus, ovaries, and prostate. The increased risk of dying from breast cancer, however, was 12% higher for every 100 mGy.
"We estimated that for every 1,000 patients treated with a standard range of doses, about 20 to 30 additional solid-cancer deaths would occur as a result of the radiation exposure,” says Cari Kitahara, Ph.D., an investigator with NCI's division of cancer epidemiology and genetics, and lead author of the study.
And the higher the dose, the higher the risk. The researchers concluded that “the risk of death from solid cancer (including breast cancer) increases with the greater absorbed dose to exposed organs and tissues. Additional studies are needed to fully weigh the risks and advantages of RAI and other major treatment options available to patients with hyperthyroidism.”
Do Other Experts Agree With the Findings?
While the results may appear worrisome, it’s important to note that some experts do not consider the findings definitive. In fact, doctors in the thyroid community are actively debating whether and how to use this new information to make treatment decisions. “There are some issues related to the publication that raise concern," says John C. Morris, M.D., a professor of medicine in Mayo Clinic's divisions of endocrinology and medical oncology.
First, Dr. Morris reports that several earlier studies did not show an increased cancer risk after RAI for hyperthyroidism. This contradicts the findings of the NCI study.
Second, the increased risk of secondary cancer after RAI for thyroid cancer is small, and some studies question whether that risk even exists. “Much higher doses of radioiodine are used to treat cancer patients,” says Dr. Morris. “The smaller doses used for the treatment of hyperthyroidism should, therefore, yield a smaller risk, but the current study does not suggest that.”
Finally, according to Dr. Morris, past studies have shown a similarly increased risk of malignancy in patients with hyperthyroidism, whether they were treated with antithyroid medication, surgery, or RAI. “This suggests that the increased risk is not related to the treatment, but rather to the disease itself,” says Dr. Morris. “The current study did not examine patients treated with surgery or medication, so it cannot judge whether what they are seeing is treatment-related.”
One thing the experts do agree on: More study is needed to understand and define any potential risks so that better treatment decisions can be made for patients with hyperthyroidism.
What Should You Do if You Are Hyperthyroid and RAI is Recommended?
According to Dr. Morris, “It's too early to recommend any dramatic changes in therapy or management of hyperthyroidism” based on concerns regarding the potential cancer risk of RAI.
RAI use is still prevalent in the U.S., but its popularity has already waned. In recent years, antithyroid drugs have increasingly been used as a first-line treatment. This shift in treatment approaches resulted from increased awareness of a link between RAI and worsening of thyroid eye disease, as well as the potential risks of radiation-induced cancers.
That said, it’s crucial for patients to know that RAI is one of three widely available treatments for hyperthyroidism and Graves’ disease. While RAI has been the favored and first-line treatment in the U.S. for decades, the two other treatments, antithyroid drugs and thyroid surgery, are more commonly used in other countries.
According to Dr. Kitahara, “We found the increased risk of death from solid cancer overall—and from breast cancer more specifically—to be modest, but RAI is still a widely used treatment for hyperthyroidism.” Your best course of action? “It’s important for patients and their physicians to discuss the risks and benefits of each available treatment option. The results of our study may contribute to these discussions,” says Dr. Kitahara.
If You Already Had RAI Treatment, What Should You Do?
If you have received RAI treatment for hyperthyroidism, and are otherwise free of symptoms, experts don’t recommend any scheduled testing to look for cancers. Be sure, however, to let your doctor know about any new symptoms or problems so they can be thoroughly evaluated.
It’s also essential for women to be diligent about regular breast-cancer screening, including mammograms.
There are no specific ways to prevent most cancers, but the American Cancer Society does recommend that you incorporate lifestyle changes that can help lower your overall risk of cancer. These include:
- Get to and stay at a healthy weight.
- Be physically active, and get at least 150 minutes of moderate activity (or 75 minutes of more vigorous exercise) each week.
- Eat a healthy diet, with a focus on plant foods.
- Avoid alcohol, or limit it to one alcoholic drink per day.