Study: GLP-1 Drugs and Breast Cancer: Results from ASCO 2026

RELEVANCE

Most relevant for: People taking or considering GLP-1 drugs.

It may also be relevant for:

• people with breast cancer
• people with metastatic or advanced cancer
• people newly diagnosed with cancer

Relevance: Medium

Strength of Science: Medium

Research Timeline: Post Approval

More rating details

Several studies presented at ASCO 2026 found that people taking GLP-1 drugs had better breast cancer-related outcomes than similar people who were not taking these medications. Researchers reported lower rates of breast cancer diagnoses in some populations and improved survival in people with early-stage and metastatic breast cancer.

These early studies suggest that GLP-1 drugs may help reduce breast cancer risk and improve survival in certain groups of patients.

Other studies have found a link between GLP-1 drugs and lower colorectal cancer risk.

What are GLP-1 drugs?

GLP-1 drugs mimic the effects of a natural hormone in your body called glucagon-like peptide-1 (GLP-1). This hormone helps regulate blood sugar, slow the pace of food moving out of the stomach and reduce appetite.

These medicines can also influence other processes in the body that may play a role in cancer prevention, which is why additional studies are being conducted.

Side effects

GLP-1 drug side effects are mostly gastrointestinal and usually most noticeable when the drugs are first started or the dose is increased.

The most frequently reported side effects include:

• Nausea (the most common)
• Diarrhea
• Constipation
• Vomiting
• Abdominal pain or bloating

People with medullary thyroid cancer shouldn’t take GLP-1 drugs. In addition, people with inherited mutations in genes that increase the risk of medullary thyroid cancer, such as RET or PTEN, should also not take GLP-1 drugs.

GLP-1 drugs and breast cancer in women

This study included more than 111,646 women ages 45 to 80 who were overweight or obese. GLP-1 use was defined as a first prescription prior to breast imaging. Of these, 15,264 had a GLP-1 prescription, while 96,382 did not.

It was not reported how long women with GLP-1 prescriptions were taking these drugs prior to breast imaging.

Researchers wanted to see whether GLP-1 drugs were linked to breast cancer risk.

 The researchers found that women taking GLP-1 drugs were less likely to be diagnosed with breast cancer than women who were not taking these medicines, although the actual number of cancers prevented was small.

Study results

 Overall, the researchers examined breast cancer cases across two different groups. The first group looked at all 111,646 women. Of these :

• 2,628 (2.4%) had breast cancer.
• 247 (1.6%) of the GLP-1 users had breast cancer.
• 2,381 (2.5%) of the non-GLP-1 users developed breast cancer.

In this large group, breast cancer was 35% less likely to occur in GLP-1 users compared to non-users.

To adjust for a possible impact of other factors on breast cancer, researchers then looked at a smaller group of 30,528 women:

• 15,264 GLP-1 users were matched to 15, 264 non-GLP-1 users
• The women were matched by age, race, ethnicity, BMI, breast density and diabetes status.
• The researchers matched each participant in one group with a similar participant in the other group (a 1:1 match) to make the groups more comparable.

The total number of breast cancer cases in this group was 600 (2.0%).

• 247 (1.6%) GLP-1 users had breast cancer.
• 353 (2.3%) non-GLP-1 users had breast cancer.

In this matched group analysis, breast cancer was 31% less likely to be diagnosed in women who took GLP-1 medications compared to women who did not.

What does this mean for me?
This study showed that women taking GLP-1 drugs were less likely to develop breast cancer compared to those who did not take these medications.

These findings are encouraging and suggest GLP-1 drugs may one day play a role in breast cancer prevention for some women. For people already using GLP-1 drugs for diabetes or weight management, these results could be reassuring and may suggest a possible added benefit. However, at the moment, experts do not recommend these medicines specifically to prevent breast cancer.

Since this was an observational study, it does not prove that GLP-1 drugs directly lowered cancer risk. More research is needed to confirm that GLP-1 drugs may reduce the risk of breast cancer.

References

McDonald ES, Gillis L, Gabriel P, et al. Association of GLP-1 agonists with breast cancer incidence in women. J Clin Oncol. 2026;44(suppl 16): abstract 10506.

McDonald ES, Gillis LB, Gabriel P, et al. GLP-1 Agonists Are Associated With a Significant Reduction in Breast Cancer Incidence in Women. JCO Oncol Pract. 2026 Jun 2. doi:10.1200/OP-26-00485

GLP-1 drugs and breast cancer in high-risk women

A second study looked at women at higher risk for breast cancer who were also overweight or obese.

Study results

Participants were high-risk women ages 18-90 with a BMI >30.

High risk was defined as having at least one of the following:

• A mutation that increases risk
• A family history of breast cancer
• Atypical ductal hyperplasia
• Atypical lobular hyperplasia
• Lobular breast cancer in situ
• Dense breasts

The study included 80,480 high-risk women. The researchers matched each of the participants who used GLP-1 medications with a similar participant who did not use GLP-1 medications. Each group included 46,581 women. GLP-1 users were matched 1:1 to non-users based on demographic, lifestyle factors, BMI and A1c levels.

Researchers followed these two groups over time.

Among participants:

• 1,164 (2,95%) of GLP-1 users developed breast cancer.
• 1,200 (3.01%) of non-GLP-1 users developed breast cancer.

These results show that breast cancer was slightly reduced in women who used GLP-1 drugs compared to women who did not.

What does this mean for me?
For women at high risk of breast cancer, especially those who are also overweight or obese, GLP-1 drugs may eventually become part of prevention discussions. For now, though, these results should be viewed as promising but preliminary rather than a standard prevention strategy. More research is needed to understand if GLP-1 drugs can be used to prevent breast cancer in those at high risk.

Reference

Gotera NP, Jones C, Gelfond J, et al. GLP-1 receptor agonists for primary prevention of breast cancer in high-risk women: A real-world analysis of efficacy and safety. J Clin Oncol. 2026;44(suppl 16): abstract 10520.

Another study looked at survival among breast cancer patients who used GLP-1 drugs after a breast cancer diagnosis compared to those who did not use GLP-1 after diagnosis.

Study results

Participants were women diagnosed with breast cancer between 2014 and 2023 who were > 18 years old. All participants had undergone a lumpectomy or mastectomy as part of their definitive breast cancer surgery.

The researchers matched each participant in one group with a similar participant in the other group (a 1:1 match) to make the groups more comparable. Participants were matched by GLP-1 use versus non-use and by age, sex, treatment after surgery (immunotherapy, chemotherapy or adjuvant endocrine therapy) and weight category (most were in the overweight or obese category).

Among participants:

• 7,249 received a GLP-1 medication for at least 3 months.
• 7,248 did not receive a GLP-1 medication.

The findings from this study show that overall survival was higher in the group taking GLP-1 drugs compared to those who did not:

• 5-year overall survival was almost 96% among GLP-1 users compared to 90% in non-users.

What does this mean for me?

For people with breast cancer, GLP-1medicines may have benefits beyond blood sugar control and weight management. However, this study only shows an association and does not prove that the GLP-1 drugs directly improved survival.

A limitation of this study was that participants were not matched by breast cancer stage. It was not known if the stage also contributed to overall survival.

More research, especially clinical trials, is needed before these findings can change treatment decisions.

Reference

Sukumar JS, Niu J, Jackson I, et al. Real-world treatment patterns and mortality associated with GLP1-RAs in breast cancer patients. J Clin Oncol. 2026;44(suppl 16): abstract 629.

Researchers in another study compared people with hormone receptor–positive, HER2-negative metastatic breast cancer who were receiving standard treatment (endocrine therapy and a CDK4/6 inhibitor) with or without GLP-1 drugs.

Study results

This study compared 604 people with metastatic breast cancer who were treated with endocrine therapy plus a CDK4/6 inhibitor alone to 604 participants who also received a GLP-1 within 3 months of starting a CDK4/6 inhibitor. Participants were matched by age, race, BMI, diabetes and type of CDK4/6 inhibitor.

The researchers wanted to know whether taking a GLP-1 was linked to breast cancer or survival.

After almost 16 months of follow-up, overall survival was:

• Almost 70 months among GLP-1 users
• Almost 50 months among GLP-1 non-users

These follow-up results show that use of GLP-1 drugs resulted in an estimated 30% lower risk of death.

What does this mean for me?

These findings are hopeful for people with this type of metastatic breast cancer who are already taking a GLP-1 for weight control. The study findings raise the possibility that GLP-1 medicines provide added benefit during cancer treatment.

However, this was observational research and does not prove that GLP-1 drugs improve survival from metastatic breast cancer. Treatment decisions should still be based on standard cancer care plus guidance from your oncology team. More research is needed before these findings can change medical care.

Reference

Palleschi M, Gianni C, Merloni F, et al. Real-world survival benefit of glucagon-like peptide-1 receptor agonists (GLP-1 Ras) concomitant with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) and endocrine therapy in hormone receptor-positive (HR+)/HER2− metastatic breast cancer: A large propensity-matched analysis. J Clin Oncol. 2026;44(suppl 16): abstract 1070.

These findings are encouraging, but they do not prove that GLP-1 drugs directly prevent breast cancer or improve survival. Since these were real-world observational studies and not randomized trials, other factors, such as weight loss, could have contributed to the results. Further, most of the studies were conducted in women who were taking GLP-1 drugs for medical reasons, such as diabetes or obesity. More research is needed to learn if these drugs work as well for people without diabetes who are not overweight. Still, the results are encouraging and suggest GLP-1 drugs may have benefits beyond weight loss and blood sugar control for some breast cancer patients.

People who are interested in understanding if a GLP-1 drug is appropriate for them should discuss the benefits and risks with their healthcare team.

Disclosure: FORCE receives funding from industry sponsors, including companies that manufacture cancer drugs, tests and devices. All XRAYS articles are written independently of any sponsor and are reviewed by members of our Scientific Advisory Board prior to publication to assure scientific integrity.

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posted 7/20/2026