Joanne Mortimer, M.D., on associations between GLP-1 use and cancer outcomes | ASCO 2026

GLP-1 receptor agonists (GLP-1s) made headlines at the 2026 American Society of Clinical Oncology (ASCO) annual meeting, with new data showing an association between GLP-1 use and significantly better outcomes in lung, breast, colorectal and liver cancers.

Lead author Mark David Orland, M.D., of Taussig Cancer Institute at the Cleveland Clinic, presented the research, which used the TriNetX Global Health Research Network to analyze data encompassing 10,225 patients with Stage I to Stage III cancer using GLP-1 agonists. The GLP-1s included liraglutide, pramlintide, dulaglutide, tirzepatide, lixisenatide or semaglutide.

GLP-1 use was associated with a 33% lower risk of death, and those with breast cancer on GLP-1s showed an even greater reduction of 45%.

In this interview, Joanne Mortimer, M.D., F.A.C.P., F.A.S.C.O., associate director for cancer research training & education coordination and vice chair and professor in the Department of Medical Oncology & Therapeutics Research at City of Hope Comprehensive Cancer Center, discusses the implications of the new data, how the conversation between oncologists and patients could shift, and emphasizes the need for more research on GLP-1s and cancer.

This interview has been edited for length and clarity.

MHE: The control group in the study was DPP4 inhibitor users, not the general population. What should oncologists and health systems or health system leaders understand about the strength of this evidence?

Mortimer: This is an association at this point, but it certainly is intriguing that there is a difference in relapse amongst these cancers. It's hard to believe that the patients on different types of glucose management medications have an increased risk, which would be the concern, but there's no reason to think that. In fact, there are a lot of data with metformin and some of these agents that there may be an advantage to being on them. But this is much more powerful because this is a real percentage decrease and seemingly a decreased risk of recurrence amongst these cancers.

It's an association, it’s intriguing, and we need to pay attention to it. I think it's going to be very hard, but the right answer is always to do a randomized clinical trial where people get GLP-1s or not. It's an impossible study to do because so many people are on these drugs and they can even get them through the mail. They get them readily, so it would be really very difficult — in this country, at least — to do a study where you're actually comparing breast cancer patients who've been treated who get a GLP-1 versus not. I think it's an association right now; it's an intriguing one biologically, and it makes sense.

MHE: Are patients who have both a cancer diagnosis and a metabolic condition getting GLP-1s at the rates that you would expect, and if not, how can that gap be addressed?

Mortimer: I think they're probably getting it more often than not, because people can now get it on their own, and it's not like you take these medications and your blood sugar drops and you're at risk. That doesn't happen, so there aren't really any adverse effects — other than the constipation and the abdominal discomfort that people sometimes get — that would keep someone from having a dangerous complication with these medications when they get them on their own through the internet, or however they get them. So, I think they're probably getting them, probably more often, although in the ideal world, you'd like people to change their diet and to exercise. But that's just probably not a realistic expectation in our society.

MHE: These data do span several tumor types, but they do come from retrospective analysis. How should oncologists communicate this kind of early signal research to patients if they're already asking about it?

Mortimer: After this presentation comes out, I'm sure patients will ask if it's going to help their prognosis, which has not been the question previously. The question has been, “Are these drugs harmful to me?” And the data that we have so far do not indicate that they're harmful. Now, these data look like it could even be helpful. We did a study from our cancer registry looking at patients who had breast cancer and were on GLP-1 agonists versus those that were not — diabetic breast cancer patients — and it turned out they had a better outcome. Again, that's not definitive, because you're looking at registry data, but so far, most of the data suggest a favorable impact of GLP-1 agonists on cancer in general and breast cancer in particular. Most of the questions we get are about whether it’s safe, and I think we all feel pretty comfortable that it's safe, and these data now are going to make them ask, “Will it help me?”

MHE: You've published on insulin resistance and breast cancer risk previously. How do these GLP-1 data connect to that earlier work, and what biological mechanism might explain the strength of the breast cancer signal specifically?

Mortimer: This is a really important question, and I don't have an answer to it. But we’ve shown that among women who have breast cancer, those that had more than had three or four elements of metabolic syndrome — those who are overweight, have pre-diabetes, metabolic syndrome, high lipids, a higher waist-to-hip ratio, or other indicators — had a higher risk of recurrence, and that was from the Women's Health Initiative Study. These were mostly older women that were in that study, but it is intriguing that that was shown, and I believe that's the case. Women who gain weight do worse, and women who have metabolic syndrome elements tend to do worse.

If we start to use GLP-1 agonists and it actually helps lipid profiles, hypertension, weight, and waist-to-hip ratios, it presumably could impact disease outcome. Obesity is a metabolically unhealthy situation, and those fat cells secrete estrogen — and people focus on that with breast cancer, but that's probably not the major mechanism why fat cells are bad for breast cancer patients. They secrete all these cytokines, all these chemicals that make cancer cells grow, and so to suppress that or to turn that around is likely to be beneficial to patients with breast cancer. But we need to keep studying this, because these drugs are just so absolutely intriguing.

MHE: Is there anything else you'd like to add?

Mortimer: There was another abstract that was presented that raised the possibility of other mechanisms, so they looked at GLP-1 receptors on cancers. These drugs are so fascinating because they have so many different effects on metabolism, and it's possible they may have a direct effect on cancer cells as well, so there's so much we need to study with these, and so far, there haven't been a whole lot of negative aspects to taking these agents, so it's a really exciting group of drugs to study for a million different reasons right now.