Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
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HYPERTHYROIDISM
Cancer risks of patients with Graves’ disease who received antithyroid drugs as initial treatment

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BACKGROUND
Graves’ disease is the most common type of hyperthyroidism. Treatment options include antithyroid drugs (ATDs) that control the hyperthyroidism and definitive treatments that destroy the thyroid (radioactive iodine therapy and surgery). The ATDs currently in use in the United States are methimazole and propylthiouracil. In recent years and for many reasons, ATDs have become the first line of treatment for patients with Graves’ disease.

Because of the many effects of thyroid hormone on cells, including increasing cell growth, there is the possibility that thyroid hormones may help cancer cells to grow. Some studies have shown that patients with hyperthyroidism have an increase chance to develop cancer, such as breast, lung, prostate and thyroid cancer. A major problem with most of those studies is that they did not consider important personal risk factors for cancer, such as smoking and obesity. Other studies looking at the link between hyperthyroidism and cancer only looked at those patients who were treated with radioactive iodine therapy, since radiation is a risk factor for cancer.

The goal of this study is to shed some light about the risk of cancer in patients with Graves’ disease who are treated with ATDs.

THE FULL ARTICLE TITLE
 Lee JY, et al. Cancer risks of patients with Graves’ disease who received antithyroid drugs as initial treatment: a nationwide population-based analysis. Thyroid 2024;34(10):1271-1279; doi: 10.1089/thy.2024.0178. PMID: 39228052.

SUMMARY OF THE STUDY
The authors looked at health information from a South Korea data base. They studied almost 30,000 patients with Graves’ disease who were treated with ATDs from 2003 to 2022. They looked at how many of these patients were also diagnosed with several types of cancer. They compared the rate of cancer on these patients with that of a control group of similar age and risk factors for cancer but without Graves’ disease. They found that patients with Graves’ disease treated with ATDs have higher chances of biliary, pancreatic, prostate and ovarian cancer as compared to the control group. The risks for those cancers were small but significant. For thyroid cancer, there was a very significant increased risk in patients with Graves’ disease, particularly within 1-2 years after starting ATDs.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Patients with Graves’ disease treated with ATDs may have higher chances of cancer as compared to healthy controls. It is possible that this increase cancer risk is due to being hyperthyroid rather than to the specific type of treatment for Graves’ disease, but this study cannot definitively answer that question. More studies are needed to clarify the relationship of hyperthyroidism, ATDs and cancer.

— Susana Ebner MD

ABBREVIATIONS & DEFINITIONS

Hyperthyroidism: a condition where the thyroid gland is overactive and produces too much thyroid hormone. Hyperthyroidism may be treated with antithyroid meds (Methimazole, Propylthiouracil), radioactive iodine or surgery.

Graves’ disease: the most common cause of hyperthyroidism in the United States. It is caused by antibodies that attack the thyroid and turn it on.

Methimazole: an antithyroid medication that blocks the thyroid from making thyroid hormone. Methimazole is used to treat hyperthyroidism, especially when it is caused by Graves’ disease.

Propylthiouracil (PTU): an antithyroid medication that blocks the thyroid from making thyroid hormone. Propylthiouracil is used to treat hyperthyroidism, especially in women during pregnancy.

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