Glucagon-like peptide-1s (GLP-1s) are best known as weight-loss drugs, but that definition is quickly expanding, according to industry experts. According to a new Penn Medicine study, these drugs show promise for lowering breast cancer risk.
Researchers led by Elizabeth McDonald, MD, PhD, a breast radiologist at the University of Pennsylvania’s Perelman School of Medicine, analyzed health records from 111,646 women aged 45 to 80 and found that those taking GLP-1 medications were roughly 30% less likely to develop breast cancer than those who weren’t. The findings, published in JCO Oncology Practice, have generated industry buzz and real questions about the capabilities of this class of drugs.
While some excitement is warranted, so is some caution, McDonald notes. “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 weightloss drugs as potential cancer prevention tools,” she says.
Stamatia Destounis, MD, FACR, FSBI, FAIUM, chair of the ACR’s Commission on Breast Imaging and a radiologist at Elizabeth Wende Breast Care in Rochester, New York, agrees that further scrutiny is needed before conclusions are drawn. Destounis is also a member or Radiology Today’s editorial advisory board. “These are interesting preliminary data. Targeted studies will need to evaluate these preliminary results,” she says. “Patients will have to be followed over time for several years to be able to really evaluate breast cancer incidence in these groups of patients with or without the GLP-1 medication.”
Tim Church, MD, MPH, PhD, CMO with Wondr Health, sees the study as part of a much larger pattern he’s been tracking around inflammation since long before GLP-1s existed. “I’ve been studying this for almost 30 years. Inflammation plays a role in everything,” he says, drawing a direct comparison to what happened in cardiology roughly two decades ago when researchers discovered that lowering inflammation reduced heart attack risk.
In addition, Church believes this is just the tip of the iceberg, and the opportunities and use cases for GLP- 1s will continue to expand. “We are all going to be on a GLP in the near future,” he says, “and it might not have anything to do with weight loss.”
A Growing Body of Evidence
While the Penn Medicine study is currently getting the most attention, it is not the only research related to the potential impact and future of GLP-1s in cancer treatment. McDonald’s study was one of multiple recent studies pointing to the need for clinical trials and further research.
In another study published in the Journal of Clinical Oncology, researchers tracked medical and prescription records of more than 10,000 patients with early-stage cancer and found GLP- 1s were associated with reduced risk in six of seven cancer types studied. Breast, liver, colorectal, and nonsmall cell lung cancers were those reaching statistical significance. For nonsmall cell lung cancer specifically, progression to stage IV disease occurred in 22.3% of patients not taking a GLP-1, compared with 10% of those who were.
A separate study, published in JAMA Network Open and led by researchers at Virginia Commonwealth University, set out to determine whether GLP-1s improve outcomes for women who already have breast cancer. Drawing on records from more than 841,000 breast cancer patients across a national research network, the study found that among women with obesity, GLP-1 use was associated with a 65% lower risk of death and a 56% lower risk of recurrence over 10 years of follow-up. The study’s authors were direct about what this may or may not prove, writing that the findings “support further evaluation of GLP-1 RA [receptor agonist] therapy in randomized clinical trials.”
An additional poster spotlight session at the 2025 San Antonio Breast Cancer Symposium added still more data points, some encouraging and some cautionary. Researchers at the University of Texas at San Antonio found that among nearly 8,800 people with breast cancer and obesity on hormonal therapy, those also taking GLP-1s had a 46% lower risk of death from any cause over roughly 5.5 years of followup. A separate analysis presented at the same session looked at more than 3,000 people with hormone receptor-positive ductal carcinoma in situ and found that GLP-1 users had a 74% lower risk of invasive or metastatic disease progression, with 93.5% surviving over five years compared with 85.7% of nonusers.
Other findings from the session were mixed. People on GLP-1s undergoing chemotherapy had fewer side effects like anemia, blood clots, and nausea, but findings suggested that GLP-1 use was linked to a higher rate of side effects from hormonal therapy itself, including hot flashes, joint pain, and osteoporosis.
Additional Data Needed
For all the buzz around the Penn Medicine findings, the study has gaps that industry experts were quick to note. For example, the analysis did not distinguish between different GLP-1 medications, account for how long individual patients had been on the drugs, or factor in genetic risk.
It’s an observational look at two populations, Destounis says, rather than a prospective study specifically looking at breast cancer incidence. “This is too early and preliminary,” she says. “We need multi-institutional prospective studies over long periods of time to draw real conclusions.”
Church says, because the study is observational rather than a randomized clinical trial, it can’t rule out the possibility that GLP-1 use is simply a marker of a certain kind of patient, rather than the driver of the outcome itself. “You could argue there’s a whole bunch of small behaviors, all adding up to a lower breast cancer risk. It wasn’t [necessarily] the medications. The medications [may be] an indication of a certain type of person,” he says, pointing to people who start GLP-1s as likely being further along what he calls the “behavioral motivational curve.”
Church isn’t dismissive of the finding but emphasizes that a randomized trial answers important questions by matching participants for age, gender, geography, and income. He expects it to hold up once trials are run, citing three reasons: the result fits with what’s already understood about GLP-1s physiologically, it’s backed by corroborating data from other recent studies, and the Penn analysis itself was large and methodologically rigorous.
Inflammation as a Common Thread
In a follow-up interview to the Penn Medicine study, McDonald told NPR that weight loss alone didn’t account for the magnitude of the observed effect. She theorizes that GLP-1s “affect many different targets and pathways associated with cancer development,” potentially including inflammation, a known driver of cancer growth.
Church is not surprised, although he recalls a time when this view around inflammation was not welcome in mainstream medicine. He specifically points to the work of Paul Ridker at Harvard, who argued that inflammation—not just cholesterol —was driving heart attacks that statistics couldn’t otherwise explain. “He got chastised for it, and he ran all these big trials, like the JUPITER trial. He showed that people with normal cholesterol but elevated inflammation could reduce the risk of heart attacks with a statin,” Church explains. “It does not surprise me that cancer, in particular breast cancer, is one of the first places we’re going to see this.”
That same open-mindedness, Church argues, needs to extend to how providers respond to studies like this one. He pushes back on the residual stigma around both weight and the medications used to treat it, rejecting the idea that when people use GLP-1s they are cheating and dismissing the notion that these drugs will “eat your muscle.” His says that weight needs to be treated “like it’s an actual clinical condition” rather than a moral failure.
In saying this, Church draws a parallel to another case where the medical establishment was slow to come around: When first presented to the field, doctors initially dismissed the idea that H. pylori bacteria, not stress or diet, caused stomach ulcers.
Implications for Breast Radiologists
While GLP-1s and cancer risk are still being sorted out in trials, Destounis says there’s already something breast radiologists are seeing play out in the exam room. Patients on GLP-1 medications are showing up for their screening mammograms having lost significant amounts of weight, and that shift is visible on the images themselves.
“Many of our patients are now coming in for their screening mammogram and are experiencing significant weight loss, so we are seeing significant changes on their imaging,” she says, pointing out that breast density can shift as a result, which could complicate the standard practice of comparing a current mammogram against a patient’s prior films.
As patients lose weight, Destounis believes imaging elsewhere in the body may get better. Ultrasound, CT, MRI, and other contrast-based studies could become more accurate and see wider use in patients who were previously overweight, since image quality and lesion visibility tend to improve once excess tissue is no longer in the way. “I am certain we will be finding significant imaging changes throughout the entire body when it comes to imaging tests,” Destounis says. “Ultrasound overall may be more accurate with weight loss and utilized more in patients that were previously overweight. The same goes for CT, MRI, and other contrast studies.”
The obvious next step, according to McDonald, is a clinical trial. She and her collaborators are working to launch a multisite study specifically designed to test whether GLP-1s reduce breast cancer incidence in high-risk women, including those with a prior breast cancer diagnosis. It’s the kind of prospective, controlled research that both Destounis and Church agree is necessary before any of this becomes clinical guidance.
Additional Possibilities
Church is watching a broader pipeline of GLP-1 development that he believes will keep pushing the conversation past weight loss. Topping his list is retatrutide, which he expects to outperform every GLP-1 on the market so far, with weight loss reaching upwards of 30%.
Notably, what he finds most striking is the route this drug is taking toward approval. “They are using, and this is just unbelievable to say this, osteoarthritis to get their FDA indication,” Church says, describing data showing a marked reduction in knee pain tied to osteoarthritis.
Beyond that, Church points to addiction and craving reduction as promising frontiers. “The addiction stuff is wild,” he says, describing early epidemiological data and some clinical evidence that GLP-1s “turn down all the cravings, including cravings for alcohol and many hard drugs.”
Dementia is also on Church’s list, although further out from showing the same promise as other areas. The first trial results were mixed, he says, but he expects the research to keep coming.
Looking ahead further, Church describes a wave of GLP-1 drugs currently working through the development pipeline that will start reaching the market over the next year or two, with competitive pressure pushing manufacturers to chase new indications, such as cancer, beyond weight loss. “This year is going to be a little bit boring,” he says. “Next year is going to be when all these studies and FDA indications start dropping.”
Whatever the cancer-specific research ultimately shows, Destounis says the case for GLP-1s rests on benefits that are already well established. “Overall reduction of weight is important for patients’ overall health—diabetes, heart disease, reduction of joint disease, and overall mobility improvement,” she emphasizes. “GLP-1s have been medications that are very important for overall health of patients, so if they also reduce breast cancer risk that would be great news.”
Ultimately, the industry goal is to find better options to prevent breast cancer, McDonald says. Outside of routine screening, doctors don’t have many ways to actually lower a patient’s odds of developing breast cancer. Preventive mastectomy is generally reserved for people with a genetic mutation that puts them at especially high risk, and tamoxifen, despite proven effectiveness, is often avoided by eligible patients because of its side effects. A medication already taken by millions of Americans, by contrast, would represent a far lower-friction option.
“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,” McDonald says.
Selena Chavis is senior director of accounts with Insenna and a Florida-based freelance writer.