Q&A with Philip Bergman, DVM, MS, PhD, DACVIM (Oncology)

For years, the decision to spay or neuter a pet was considered a straightforward milestone of responsible ownership. However, a recent "explosion" of literature has sparked a heated debate, often leaving pet owners caught between the anecdotal advice of breeders and the clinical recommendations of their veterinarians.

In this interview with dvm360 following his lectures at the 2026 Veterinary Meeting & Expo, Philip Bergman, DVM, MS, PhD, DACVIM (Oncology), shares insights into the current landscape of research regarding spay and neuter and the cancer risks associated with the procedures. Throughout the interview, Bergman shares some intel on the actual risks based on current research, and how it can vary, educating clients, and the disconnect between what breeders are telling clients, and what clients are listening to from their veterinarians.

Below is a transcript from the interview, edited lightly for clarity

dvm360: Why do you think there has been an “explosion” of publications investigating a possible connection between cancer and spay/neuter?

Philip Bergman, DVM, MS, PhD, DACVIM (Oncology): I think there's several reasons. One, I think breeders felt very strongly about this because of what they were potentially seeing with them and their clients and the folks that were buying those dogs and cats from them. And often science slowly catches up with what's happening anecdotally. Part of why I started doing this talk, it was probably 5 or 6 years ago, so just before the pandemic, was 1) there was an explosion of literature. And some of that scientific literature wasn't very good, to be honest, and it was often the studies that a lot of breeders were quoting, and that kind of bothered me, because I felt like, at least up here in the northeast, we're north of New York City, we often will have these clients that will walk in with a stack of paper from their breeder that says to do this and not do that. And it bothered me that they owned that conversation with the owner.

I felt like [veterinarians] should actually be the ones that own that conversation. It's fine if they want to have input, but veterinarians are much more trained to evaluate the scientific literature. I quickly learned that my PhD, even though I have various projects that I was working on, was really to train me how to read the scientific literature.

That was kind of eye-opening when I finally realized that during the PhD, they were sinking a huge amount of time, energy and focus into training me how to evaluate the literature, and so some of the articles that the breeders were really staunchly part of showed a 3 to 5 fold increase in lymphoma, mast cell, and hemangiosarcoma and being a clinician scientist, I started to look at the literature more closely before I developed the lecture. And it became very apparent to me that while I think there could be some truth in the hemangiosarcoma side of things, based on some of the other scientific literature out there, especially the Golden Retriever Lifetime Study that shows that—at least at that time, and it's likely even more now—8% of those golden retrievers were being diagnosed with hemangio, which is frightening when you think about it, because that that's on my Top 5 hated list of tumors. We struggle to know how to treat those effectively. And if you look outside of hemangio the very best studies that are out there are with 1000s of dogs so it becomes infinitely more trustable whereas the breeder-specific studies that they were talking about. Those would often have 10 dogs for each specific type of tumor. And that’s hard for me to hear, because you're making global recommendations based on 10 dogs with lymphoma, 10 dogs with hemangio, 12 dogs with mast cell, etc.

So in the context of lymphoma, there's a study out there that I think is very trustable, that shows there's about a 30% increase in risk for female dogs that are neutered. But interestingly, that same exact study showed that there was about a 40% decrease in male dogs. So, it can go both ways, but that's very different than the 3 to 5 fold that we talked about that the breeders like to quote.

The other one that was eye-opening to me when I started to dig into the data was on mast cell tumors, so something that oncologists see left and right.

There were 2 very important studies in some of the very best studies, which again had thousands of dogs in them, so were infinitely more trustable than some of the other data that we just talked about. There was one out of North Carolina State, and another one that was being done with Antech that showed that there was about a 2.5 fold reduction in risk associated with neutering, not a 3-to-5-fold increase. So it was the exact opposite.

What I then started to realize was I need to make a continuing education lecture about this to basically arm veterinarians with the data and what I really try to do in that talk, and I really like it, because, one, it's changing over time as new data comes in, but veterinarians have so far been super appreciative of that, because that took me probably a week to put all of that information together—what general practitioner is going to take that amount of time to research something like that?

So I felt like my job was to pass that information on to the veterinarian, and then they make that review of whether it makes sense or not. And so I walk people through in a very evidence-based medicine way to talk about the literature.

I characterize the data as strongly beneficial to research. I then do moderate level of trust, and then start to get down to the ones that I don't trust because there's so few patients and basically the summary was that it does appear to be an increase in hemangio, and that's trustable. There is an increased risk associated with urothelial tumors, so things like transitional cell carcinoma of the bladder, that's trustable as well. And then the hemangio data that we just talked about, whereas nearly everything else, and there's, I should also add osteosarcoma probably to that list, but the vast majority of that work is in Rottweilers, so we don't know if that can extrapolate over to other breeds.

And so I spent a lot of time reviewing that literature in that lecture. Then I also point out there's a lot more literature in the context of osteoarthritis, intervertebral disc disease, cruciate ligament rupture, that type of thing. And so when you're trying to make patient-specific recommendations, I tried to show a sense of urgency to say, slow down if you're going to make those decisions based on cancer, because the data is not as good as some of the data that's out there with, again, osteoarthritis, cruciate ligament, intervertebral disc disease.

That said what you can glean from the literature is: Rotties that are neutered early do appear to have very significant increases in osteosarcoma, and that is work out of Purdue University. Again, it looks like there is a neuter association for Golden Retrievers with hemangiosarcoma. But this global thought that, again, breeders keep perpetuating of 3-5-fold increases in hemangios based on the total extent of publications that are out there.

So, long-winded answer to say, it's complicated, like most things in biology.