A new study is weighing the risks and benefits of radioactive iodine treatment in thyroid cancer patients. The study, published in the New England Journal of Medicine, suggests that surgery alone may be the best course of action for patients who fit the “low risk” category.

Researchers looked at more than 700 patients with small, well differentiated thyroid cancer who underwent surgical resection of their tumor. The study included adults with tumors no larger than 2 cm, who had no lymph node involvement.  Results showed that patients who were treated with surgery alone did not have worse outcomes than patients who followed their surgery with radioactive iodine treatments.

In RCT involving patients with low-risk differentiated thyroid cancer undergoing thyroidectomy, a follow-up strategy that did not involve the use of radioiodine was noninferior to the use of radioiodine in the response to treatment at 3 years. https://t.co/RaJL3tdE4T pic.twitter.com/8nIPw50nkg

— NEJM (@NEJM) March 9, 2022

According to Dr. Bryan McIver, deputy physician-in-chief at Moffitt Cancer Center and senior member in the Endocrine Oncology Program, Moffitt has recognized for at least a decade that most thyroid cancers are low risk, with excellent outcomes following surgery by an experienced, specialist surgeon.  At Moffitt, thyroid cancer patients are considered low risk if they are 55 and younger, with tumors smaller than 2 cm and contained within the thyroid and with few or no lymph nodes involved in the cancer.  Some older patients may also fall into the low-risk category, but patients with invasive cancer, or cancer that has spread more widely, remain at higher risk for bad outcomes from the disease.

“Our low risk patients have essentially normal life expectancy following surgery alone,” said McIver. “However, there is an important need for careful follow-up because of high rates of recurrence of the disease, reaching as much as 20-30% for cancers that have spread into regional lymph nodes, especially in the sides of the neck as opposed to the area behind the thyroid gland.”

So what are the risks of using radioactive iodine to treat thyroid cancer patients? More importantly, do those risks outweigh the rewards?

According to McIver, radioactive iodine can injure saliva glands, causing dry mouth and increasing the risk of later periodontal disease. It can also damage the tear ducts, causing dry and/or watering eyes. It is also harmful to unborn children, so it should never be given to women who are pregnant or might be pregnant.

“The biggest worry is the risk of causing other types of cancer. Several large, retrospective studies suggest that high doses of this agent can increase the risk of colon cancer, gynecological cancer and some blood cancers,” said McIver. “Although these risks are not very large, they do need to be considered and weighed in the balance of risk and benefit as we tailor and design an individual treatment plan for a patient with thyroid cancer.  The potential benefit must always exceed the possible harm.”

"Although these risks are not very large, they do need to be considered and weighed in the balance of risk and benefit as we tailor and design an individual treatment plan for a patient with thyroid cancer.  The potential benefit must always exceed the possible harm."

- Dr. Brian McIver, Deputy Physician-In-Chief

Moffitt doctors are highly selective in their use of radioactive iodine treatments, targeting it toward patients either at risk of death from the cancer, or at high risk of recurrence.

“Over the last decade, our treatment of patients like those in the study already conforms to their recommendation, to avoid the use of radioactive iodine,” said McIver. “Although it was controversial at the time, we based our decision on very solid evidence from large retrospective studies.  This new study is wonderful validation for our approach, which can now be based on a true, prospective clinical trial.”