Popular Weight-Loss Injections Are Now Being Tested in Cancer Treatment

Demand for weight-loss drugs has risen rapidly in recent years. Anti-obesity medicines such as semaglutide (Wegovy) and tirzepatide (Zepbound, Mounjaro) are making a major difference in weight loss. Commonly known as glucagon-like peptide 1 (GLP-1) agonists, they offer potential benefits beyond obesity, including type 2 diabetes, inflammation, and depression. But could these drugs also be used in cancer treatment?

Obesity can reduce cancer treatment effectiveness and increase treatment-related adverse effects. Some oncologists have therefore begun cautiously using anti-obesity drugs in cancer patients and investigating their effects.

Weight-Loss Injections and Cancer Treatment

These injections mimic glucagon-like peptide-1 (GLP-1), a naturally occurring hormone that increases insulin secretion.

How They Work:

The main effects of GLP-1 agonists include:

• Increased Insulin Secretion: Glucagon-like peptide-1 agonists stimulate pancreatic beta cells, increasing insulin secretion after eating. This controls blood glucose rises more quickly and effectively.
• Reduced Glucagon Secretion: GLP-1 agonists reduce glucagon release in the liver. Glucagon raises blood glucose, so reduced secretion helps lower it.
• Slower Gastric Emptying: GLP-1 agonists slow stomach emptying, prolonging fullness and reducing food intake, which may support weight loss.
• Improved Beta-Cell Function: GLP-1 agonists improve pancreatic beta-cell function, reducing insulin resistance and helping protect beta cells.

These glucose-regulating processes also support weight loss. Drugs such as Wegovy and Zepbound slow gastric emptying and prolong fullness. Because they can increase nausea and vomiting with chemotherapy, however, they are generally preferred during maintenance treatment.

Before exploring the details, here are FDA (United States Food and Drug Administration)-approved injectable medicines used for weight loss:

Dr. Neil Iyengar, a breast oncologist at Memorial Sloan Kettering Cancer Center, says these medicines may be used for patients at the threshold of obesity. He believes weight loss may improve cancer outcomes and anti-obesity drugs could be promising for some patients.

GLP-1 Agonist Effectiveness in Cancer Patients

GLP-1 agonist use in cancer patients is based on limited studies. Small retrospective studies, particularly in breast cancer patients receiving aromatase inhibitors, show that these medicines produce less weight loss in cancer patients than in the general population. For example, a study presented at the 2024 ASCO (American Society of Clinical Oncology) meeting investigated GLP-1 agonists in 75 women with breast cancer. Of these, 80% had diabetes and 60% were receiving hormone therapy. After treatment, mean weight loss was 6.2 kg (5%). In patients without cancer, the proportion was twice as high.

Another study found that Wegovy reduced body mass index (BMI) by 4.34% in breast cancer patients versus 14% in the general population. BMI increased with Zepbound in cancer patients, whereas a 15% reduction was reported in the general population. These findings indicate substantially reduced weight-loss effectiveness of GLP-1 agonists in cancer patients.

Safety and Future Research

Thyroid C-cell tumors are a major safety concern with GLP-1 agonists. Both drugs were considered unsuitable for patients at risk of thyroid cancer. Recent studies, however, have shown no increase in thyroid cancer risk. Doctors nevertheless continue to monitor thyroid and other tumors closely.

Although some oncologists consider GLP-1 agonists safe, they emphasize caution particularly in cancer patients who have had bariatric (weight-loss) surgery. Risks such as delayed gastric emptying and intestinal obstruction may be greater in these patients.

Larger, multicenter, global phase 3 trials are planned to evaluate GLP-1 agonists in cancer patients. These will test efficacy and safety. If they produce significant, sustained weight loss, the drugs could potentially receive FDA approval for this setting.

Conclusion: Could This Be a Major Advance in Obesity and Cancer Treatment?

Dr. Iyengar believes that successful weight management with these drugs in cancer patients could be among the greatest advances in medicine and oncology. Yet their lower effectiveness than in the general population makes further research essential. Anti-obesity medicines could transform cancer care, but much work remains.

The relationship between weight loss and cancer has long been debated. Early data are promising, although it is not yet clear whether GLP-1 agonists offer a solution. Further research on efficacy and safety in cancer patients is needed. Managing obesity could improve general health outcomes and perhaps treatment responses.