By Xavier Martinez
The world's most popular weight-loss and diabetes drugs are linked to a powerful new possible benefit: better outcomes for cancer patients.
A suite of four new studies suggest that people taking so-called GLP-1 drugs like Novo Nordisk's Ozempic and Eli Lilly's Mounjaro saw reductions in tumor progression, lower overall chance of death and less risk of developing breast cancer.
"It's really provocative that they showed, in several cancers, that people who took these drugs seem to have a lower risk of their cancer returning," said Dr. Jennifer Ligibel, a breast oncologist at the Dana-Farber Cancer Institute who wasn't involved in any of the studies.
One study from researchers at the Cleveland Clinic Cancer Institute tracked more than 10,000 patients with early-stage cancers who started GLP-1 drugs after diagnosis and compared their disease progression to those on a different diabetes medication. Those on GLP-1s were less likely to see their cancer spread.
In lung cancer patients, the rate of progression to advanced disease was cut roughly in half -- 10% in GLP-1 users versus 22% in the comparison group. Breast cancer patients showed a similar pattern, with progression rates of 10% versus 20%. Colorectal and liver cancers also showed statistically significant reductions.
Given millions of Americans are on GLP-1s, "it's obviously quite important that we immediately understand what the potential anti-tumor effects could be," said Dr. Mark Orland, a resident at Cleveland Clinic who will present the study at the American Society of Clinical Oncology annual meeting later this month.
A cancer impact would add to the health benefits that researchers credit to GLP-1 drugs. In addition to reducing blood sugar and spurring weight loss, the medicines are approved for reducing the risk of heart attacks and strokes, and in testing for helping with sleep apnea and dampening addictive behaviors. The drugs have also turned Novo Nordisk and Eli Lilly, their makers, into two of the world's most valuable drug companies. Yet heavy demand has stressed companies and governments that have to cover the costs.
These studies were observational, which differs from research done on drugs to study intended effects. Instead people in these studies were already taking the drugs for diabetes or obesity and researchers gleaned insights from their medical records. Further research needs to be done to confirm the results.
Other studies specifically looked at breast cancer, examining both whether GLP-1 users were less likely to develop the disease and whether they lived longer after diagnosis. An analysis from the University of Texas MD Anderson Cancer Center of more than 137,000 breast cancer patients found that more than 95% of GLP-1 users were alive after five years, compared with 89.5% for nonusers.
A University of Pennsylvania study of nearly 95,000 women undergoing breast imaging found those who had taken a GLP-1 drug were about 25% less likely to be diagnosed with breast cancer, even after accounting for age, weight and other risk factors.
"We're seeing a signal across databases which is certainly interesting because all of these studies have slightly different designs," said Dr. Jasmine Sukumar, a breast oncologist at UT MD Anderson and researcher on the study examining GLP-1 use and breast cancer survival.
Scientists don't yet know why the drugs might be having this effect. One theory is that GLP-1s reduce cancer risk indirectly -- by driving weight loss and improving metabolic health, both of which are independently linked to lower cancer rates. The other is more direct: receptors for GLP-1, the hormone these drugs mimic, appear on the surface of some tumor cells, raising the possibility that the drugs are acting on cancer biology itself.
As of now, neither Eli Lilly nor Novo Nordisk are studying their GLP-1 drugs in relation to cancer.
The researchers say these findings show an association, not direct causality. The four papers relied on retrospective reviews of insurance claims and medical databases. Patients who are prescribed GLP-1 drugs tend to have more access to healthcare and more consistent follow-up than those who aren't -- advantages that could independently improve their outcomes.
Randomized controlled trials, which assign patients to treatments by chance and more tightly control for differences in income, background health and medical access, are what is normally used to determine whether the drugs themselves are driving the benefit.
Despite those limitations, the consistency of the data across hundreds of thousands of patients marks a possible new frontier for the pharmaceutical industry's most lucrative drug class.
"It's hard to ignore the numbers," said Dr. Jaroslaw Maciejewski, vice chair of the Cleveland Clinic Cancer Institute, whose lab led one of the studies.
Write to Xavier Martinez at xavier.martinez@wsj.com
(END) Dow Jones Newswires
May 21, 2026 17:00 ET (21:00 GMT)
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