New research links GLP-1 medications to a 30 percent reduction in breast cancer risk — and a second study explains why the drug will stay out of reach for much of the world.
The waiting room at a breast imaging center looks the same almost everywhere: a row of chairs, women in paper gowns, a machine humming somewhere down the hall. What has changed, in the last few years, is what some of those women are carrying in their purses — a prescription for Ozempic or Wegovy, taken for weight loss or blood sugar control or both. And now, as of this week, a reason to wonder whether that prescription might be doing something else entirely.
A retrospective analysis of more than 111,646 women between the ages of 45 and 80, presented at the 2026 American Society of Clinical Oncology Annual Meeting, found that those taking GLP-1 medications were about 30 percent less likely to develop breast cancer than those who were not. The study was led by Elizabeth McDonald, MD, PhD, a professor of radiology at the University of Pennsylvania Perelman School of Medicine and a practicing breast radiologist at Penn’s Abramson Cancer Center. The results were also published in JCO Oncology Practice.
“While our study was observational and does not definitively confirm an association between GLP-1 medications and reduced breast cancer incidence, it does add to the growing body of evidence suggesting that it’s worth investigating these weight-loss drugs as potential cancer prevention tools,” McDonald said.
GLP-1 medications — which mimic a natural hormone that regulates blood sugar and appetite, originally developed for type 2 diabetes and now widely used for weight management — have attracted growing attention in oncology for reasons that go well beyond the established link between excess body weight and cancer. The drugs reduce systemic inflammation through multiple pathways and carry metabolic and epigenetic effects that researchers believe may inhibit tumor growth directly. The Penn analysis found statistically significant results across two separate cohort analyses: a 35.1 percent lower odds of breast cancer in the full group and a 30.5 percent lower odds in a matched cohort of 30,528 women controlled for age, race, ethnicity, BMI, breast density, and diabetes status.
The researchers are not claiming cause and effect — only that the signal is consistent and strong enough to justify a clinical trial, which McDonald and her collaborators are now working to establish. “GLP-1 medications are intriguing from a cancer research perspective because they weren’t designed for cancer therapy, but they do affect many different targets and pathways associated with cancer development, so we’re eager to study them in this context,” McDonald said.
Breast cancer prevention options are notably limited; Tamoxifen is highly effective at reducing incidence in high-risk patients, but uptake remains low given its side effects. Prophylactic mastectomy is appropriate for some with certain genetic mutations, but is not broadly applicable. GLP-1 medications, by contrast, are already taken by millions of Americans — which makes the cancer signal worth pursuing.
“There are at least 13 types of cancer we know are linked to obesity, including post-menopausal breast, colon and gastric (stomach), prostate, endometrial, and others,” Sherry Shen, MD, a breast medical oncologist at Memorial Sloan Kettering Cancer Center who studies the relationship between obesity, metabolic health, and GLP-1 medications, told MSK’s On Cancer. “These medications look to be promising in potentially reducing the number of people who are diagnosed with these obesity related cancers.”
“Ultimately, we want to find better options to prevent breast cancer,” McDonald said. “It’s been encouraging to see the survival rates for breast cancer improve over recent decades, and we’d love to see the same gains in prevention.”
No generic GLPs on the horizon
There is a complication embedded in all of this, and a second study published last week in JAMA Health Forum makes it plain. GLP-1 drugs are biologics — large, protein-sized molecules manufactured in living cells, unlike the small-molecule compounds that make up nine out of 10 prescriptions filled in the U.S. Traditional generic drugs have transformed the pharmaceutical landscape over the past 30 years, saving trillions of dollars for hundreds of millions of patients, precisely because regulators can lean on the safety and efficacy record of the brand-name drug to approve a chemical copy. Biosimilars, the biologic equivalents, are harder to manufacture and far harder to evaluate — and new research from UC San Francisco shows how uneven the global framework for approving them actually is.
Only five percent of prescriptions are for biologics like Ozempic, but they make up more than half of all drug spending, Jonathan Watanabe, PharmD, MS, PhD, chair of the UCSF Department of Clinical Pharmacy and first author of the paper, said. “Yet many countries aren’t equipped to quickly vet and approve of new biosimilars, limiting access for patients.”
Watanabe and his colleagues analyzed biosimilar approval frameworks across 19 countries, including the U.S., Canada, the United Kingdom, Nigeria, Brazil, Egypt, and Indonesia. Most countries used similar language to describe biosimilars at the outset, but their rules quickly diverged: some accepted laboratory similarity as sufficient for approval, while others demanded patient trials; some authorized pharmacists to substitute a biosimilar at the pharmacy counter, while others required the prescribing doctor to write an entirely new prescription; some drew on data from trusted foreign regulators, while others required companies to repeat studies locally. The fragmentation slows market entry and keeps prices high — the same structural problem that delayed affordable access to HIV treatments, hepatitis C drugs, and cancer therapies in previous decades.
“Generics represent one of the biggest success stories of the pharmaceutical industry in terms of making life-extending treatments more affordable, and we hope our study helps biosimilars do the same,” Watanabe said. The researchers argue that aligning those standards globally could replicate the generics effect for biologics. Until that alignment happens, the drug now showing such promise in breast cancer prevention will remain, for much of the world, the kind of medicine most people cannot afford.
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