Semaglutide Risk: Recent Iowa Study Shows Potential Tumor Growth Risk in Rare Cancers

One week, the data says GLP‑1s might shrink breast tumors. The next, we look at a study from the University of Iowa suggesting that semaglutide might accelerate certain neuroendocrine tumors.

If you’re feeling a little whiplash, you’re not alone. This is the frontier of medicine, where the same class of drug can look like both a miracle and a question mark.

Let’s talk about what this recent study actually showed, what it didn’t, and why it deserves your attention even if you’ve never heard the term “neuroendocrine neoplasm” in your life.

The March 2025 study: What we now know

Researchers at the University of Iowa, where I’ve been treated as a patient myself and where my wife and children have also received care, looked at six human models of neuroendocrine tumor cells. Half of them had high levels of GLP‑1 receptors, which are the same receptors that semaglutide (Ozempic, Wegovy) and other GLP‑1 meds target.

When those cells were exposed to semaglutide:

• Two tumor lines showed 19% and 22% faster growth in the lab

• In mice implanted with one of those tumors, semaglutide led to a 72% increase in tumor size

That’s not nothing. And if that makes you pause, it should.

But we need context.

What this does not mean

• It does not mean GLP‑1 drugs cause cancer. The study did not show that

• It was not a human trial. This was done in cell models and mice

• Neuroendocrine tumors are rare. Only some of them express GLP‑1 receptors

This kind of data is more about raising questions than delivering conclusions. But when millions of people are now taking these medications, even the early questions matter.

There is a precedent for concern

If you’ve read the fine print, you already know that GLP‑1 medications carry a black box warning for medullary thyroid carcinoma, another rare neuroendocrine tumor. That warning has always been more of a better safe than sorry situation, based on animal studies, and strong post-marketing data. But this new research brings those concerns closer to home.

That said, this study does not change the benefit versus risk equation for most people. It does, however, highlight how much we still don’t know.

The bigger story: GLP‑1s give and GLP‑1s take away

It’s not lost on me that just days ago, we were covering early research on tirzepatide shrinking breast tumors in mice. That was hopeful, and maybe even exciting.

Now this new study out of my own home state pulls us in the other direction. Once again, we are looking at a lab model. Once again, we are looking at a rare tumor. And once again, it is far too early to panic.

But the contrast is hard to ignore.

That’s where we are with GLP‑1s. They are changing lives. They are improving metabolic health, reducing food noise, lowering cardiovascular risk, and for many people, offering a shot at a longer life. But they are not magic. And they are not yet fully understood.

So when headlines swing from cancer cure to tumor risk, just remember this, both stories can be true. Because both are happening in controlled lab environments, not in human patients.

So what should you do with this information?

• If you’ve been diagnosed with a neuroendocrine tumor, or if you have a family history of rare endocrine cancers, it may be worth having a conversation with your doctor

• If you’re on a GLP‑1 and this freaks you out, take a breath. Most people will never deal with the type of tumor this study looked at

• But if we want to be taken seriously as a patient community, we have to be willing to look at all the data, even the uncomfortable stuff

Because informed consent only works when the information is complete.

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