BACKGROUND
Graves’ disease is the most common cause of hyperthyroidism in the United States. It can be treated with antithyroid medication, radioactive iodine therapy or thyroidectomy (thyroid surgery). For many years, radioactive iodine therapy was the most common treatment for Graves’ disease in the United States. It works because the thyroid is the only tissue in the body that takes up and concentrates iodine within the gland. When iodine is radioactive with a certain isotope (I131), the radiation destroys thyroid cells, shrinking the size of the thyroid and often results in permanent hypothyroidism. Radioactive iodine therapy is also used to treat thyroid cancer.

Whenever radiation is involved, there is a concern that it may increase the risk of cancer in the cells that are exposed to the radiation but were not killed off. Indeed, studies have demonstrated a link between radioactive iodine therapy treatment for thyroid cancer and a slight increased long-term risk for other cancers in the body. However, a much lower dose of radioactive iodine therapy is used in the treatment of Graves’ disease. A few studies have looked at the association between radioactive iodine therapy for hyperthyroidism and long-term cancer risk and the results are variable.

This study specifically reviews the risk of identifying thyroid cancer in patients with Graves’ disease who underwent thyroid surgery and compares the data between patients who previously received radioactive iodine therapy and those who did not.

THE FULL ARTICLE TITLE
Ramesh S, et al. Malignancy risk associated with radioactive iodine therapy for Graves’ disease. Am J Surg 2024;241:116075; doi: 10.1016/j.amjsurg.2024.116075. PMID: 39546855.

SUMMARY OF THE STUDY
Researchers reviewed data from the charts of 413 patients with Graves’ disease who had undergone thyroid surgery. Overall, 38 patients had received radioactive iodine therapy prior to surgery (treated group) and 375 had not (non-treated group). The reason for surgery was more likely to be for the management of a thyroid nodule or cancer in the treated group (37% and 13% respectively) compared to the non-treated group (12% and 9% respectively).

Both groups had a similar number of thyroid nodules seen prior to surgery. Following surgery, after looking at the thyroid gland under the microscope, there was a similar rate of cancer seen in both groups. The size of the thyroid cancer in the treated group tended to be larger than the thyroid cancer seen in the non-treated group (1.65 vs 0.7 cm)

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that patients with Graves’ disease who were treated with radioactive iodine therapy and subsequently underwent thyroid surgery had a similar rate of thyroid cancer seen on the surgical specimen compared to those who did not undergo prior radioactive iodine therapy. Thus, it appears that radioactive iodine therapy for Graves’ disease does not increase the risk for thyroid cancer. However, the study does not include a comparison with patients who received radioactive iodine therapy and did not require surgery and therefore does not provide information about the risk of thyroid cancer in all patients with Graves’ disease who were treated with radioactive iodine therapy. Further research is required to help evaluate the question about the risk for thyroid cancer related to radioactive iodine therapy for hyperthyroidism.

— Poorani Goundan, MD

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