With #Ozempic and #ozempicweightloss continuing to trend on social media, along with the mainstream media focusing on celebrities who rely on Ozempic (semaglutide) for weight loss, the daily requests for this new medication have been increasing.
Accompanying these requests are concerns and questions about potential risks, including this most recent message from one of my patients: “Dr. P – I saw the warnings. Is this medication going to make me get thyroid cancer? Please let me know!”
Let’s look at what we know to date, including recent studies, and how to advise our patients on this very hot topic.
Using GLP-1 receptor agonists for obesity
We have extensive prior experience with glucagon-like peptide 1 (GLP-1) receptor agonists, such as semaglutide, for treating type 2 diabetes and now recently as agents for weight loss.
Large clinical trials have documented the benefits of this medication class not only for weight reduction but also for cardiovascular and renal benefits in patients with diabetes. The subcutaneously injectable medications work by promoting insulin secretion, slowing gastric emptying, and suppressing glucagon secretion, with a low risk for hypoglycemia.
The Food and Drug Administration approved daily-injection GLP-1 agonist liraglutide for weight loss in 2014, and weekly-injection semaglutide for chronic weight management in 2021, in patients with a body mass index ≥ 27 with at least one weight-related condition or a BMI ≥ 30.
The brand name for semaglutide approved for weight loss is Wegovy, and the dose is slightly higher (maximum 2.4 mg/wk) than that of Ozempic (maximum 2.0 mg/wk), which is semaglutide approved for type 2 diabetes.
In trials for weight loss, data showed a mean change in body weight of almost 15% in the semaglutide group at week 68 compared with placebo, which is very impressive, particularly compared with other FDA-approved oral long-term weight loss medications.
The newest synthetic dual-acting agent is tirzepatide, which targets GLP-1 but is also a glucose-dependent insulinotropic polypeptide (GIP) agonist. The weekly subcutaneous injection was approved in May 2022 as Mounjaro for treating type 2 diabetes and produced even greater weight loss than semaglutide in clinical trials. Tirzepatide is now in trials for obesity and is under expedited review by the FDA for weight loss.
Why the concern about thyroid cancer?
Early on with the FDA approvals of GLP-1 agonists, a warning accompanied the products’ labels to not use this class of medications in patients with medullary thyroid cancer, a family history of medullary thyroid cancer, or multiple endocrine neoplasia syndrome type 2. This warning was based on data from animal studies.
Human pancreatic cells aren’t the only cells that express GLP-1 receptors. These receptors are also expressed by parafollicular cells (C cells) of the thyroid, which secrete calcitonin and are the cells involved in medullary thyroid cancer. A dose-related and duration-dependent increase in thyroid C-cell tumor incidence was noted in rodents. The same relationship was not demonstrated in monkeys. Humans have far fewer C cells than rats, and human C cells have very low expression of the GLP-1 receptor.
Over a decade ago, a study examining the FDA’s database of reported adverse events found an increased risk for thyroid cancer in patients treated with exenatide, another GLP-1 agonist. The reporting system wasn’t designed to distinguish thyroid cancer subtypes.
Numerous subsequent studies didn’t confirm this relationship. The LEADER trial looked at liraglutide in patients with type 2 diabetes and showed no effect of GLP-1 receptor activation on human serum calcitonin levels, C-cell proliferation, or C-cell malignancy. Similarly, a large meta-analysis in patients with type 2 diabetes didn’t find a statistically increased risk for thyroid cancer with liraglutide, and no thyroid malignancies were reported with exenatide.
Two U.S. administrative databases from commercial health plans (a retrospective cohort study and a nested case-control study) compared type 2 diabetes patients who were taking exenatide vs. other antidiabetic drugs and found that exenatide was not significantly associated with an increased risk for thyroid cancer.
And a recent meta-analysis of 45 trials showed no significant effects on the occurrence of thyroid cancer with GLP-1 receptor agonists. Of note, it did find an increased risk for overall thyroid disorders, although there was no clear statistically significant finding pointing to a specific thyroid disorder.
Differing from prior studies, a recent nationwide French health care system study provided newer data suggesting a moderate increased risk for thyroid cancer in a cohort of patients with type 2 diabetes who were taking GLP-1 agonists. The increase in relative risk was noted for all types of thyroid cancer in patients using GLP-1 receptor agonists for 1-3 years.
An accompanying commentary by Caroline A. Thompson, PhD, and Til Stürmer, MD, provides perspective on this study’s potential limitations. These include detection bias, as the study results focused only on the statistically significant data. Also discussed were limitations to the case-control design, issues with claims-based tumor type classification (unavailability of surgical pathology), and an inability to adjust for family history and obesity, which is a risk factor alone for thyroid cancer. There was also no adjustment for exposure to head/neck radiation.
While this study has important findings to consider, it deserves further investigation, with future studies linking data to tumor registry data before a change is made in clinical practice.
No clear relationship has been drawn between GLP-1 receptor agonists and thyroid cancer in humans. Numerous confounding factors limit the data. Studies generally don’t specify the type of thyroid cancer, and they lump medullary thyroid cancer, the rarest form, with papillary thyroid cancer.
Is a detection bias present where weight loss makes nodules more visible on the neck among those treated with GLP-1 agonists? And/or are patients treated with GLP-1 agonists being screened more stringently for thyroid nodules and/or cancer?