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What My Patients Are Asking: Can Dog Deworming Medicine Treat Breast Cancer?
Brian Wojciechowski, M.D.
August 30, 2019

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Brian Wojciechowski, M.D., practices medical oncology in Delaware County, Pennsylvania at Riddle, Taylor, and Crozer hospitals and also serves as's medical adviser. A native of South Philadelphia, he trained at Temple University School of Medicine and Lankenau Medical Center. Dr. Wojciechowski is a sought-after speaker on the topics of medical ethics and the biology of cancer.

Blogs and popular media have discussed using fenbendazole (brand names: Panacure, Safe-Guard), a drug used to deworm dogs, to treat cancer. While some studies on cells in petri dishes and in mice suggest that fenbendazole might have anti-cancer properties, no studies have been done in people and it’s not clear what side effects it may cause or what the optimal dose might be.

Listen to the podcast to hear Dr. Wojciechowski talk about:

  • the type of drug fenbendazole is and how it might kill cancer cells
  • the studies in petri dishes and mice on fenbendazole that have been done so far
  • what he tells his patients when they ask about fenbendazole

Running time: 14:58

Thank you for listening to the podcast. Please subscribe on iTunes, Stitcher, Spotify, TuneIn, or wherever you listen to podcasts. To share your thoughts about this or any episode, leave feedback on the podcast episode landing page on our website.

Show Full Transcript

Jamie DePolo: Hello! Thanks for listening! Our guest today is Brian Wojciechowski, M.D., who practices medical oncology in Delaware County, Pennsylvania, at Riddle, Taylor, and Crozer hospitals and also serves as’s medical adviser. A native of South Philadelphia, he trained at Temple University School of Medicine and Lankenau Medical Center. Dr. Wojciechowski is a sought-after speaker on the topics of medical ethics and the biology of cancer.

In this What My Patients Are Asking podcast, we’re going to talk about stories in the popular media about using fenbendazole, a drug used to deworm dogs, to treat cancer. Dr. Wojo, welcome to the podcast!

Dr. Wojciechowski: Thank you, Jamie. Thanks for having me!

Jamie DePolo: Of course. Now I personally have used fenbendazole to treat one of my dogs that had hookworms, and in our stage IV metastatic Discussion Board forums, some people have been talking about using that drug, fenbendazole, to treat cancer. In the stores, fenbendazole is sold as Panicure and Safeguard, and it’s used to treat a variety of parasites, as I said, including roundworms, hookworms, and whipworms, in dogs, and I think there are some studies in petri dishes that suggest that fenbendazole might have anti-cancer properties. I don’t know of any studies done in people. I did kind of a quick search. So, can you tell us, Dr. Wojo, a little bit about the drug? What does it do in the body, and I guess what I’m thinking most importantly, is this really safe for people to be taking?

Dr. Wojciechowski: Yeah, there’s a lot of good questions wrapped up in there, and I will just start by saying that fenbendazole is a drug that I was already familiar with because I have given it to my dogs, as you have. The technical name for the drug, for the class of drugs, is anthelmintic, a fancy way of saying that it kills worms. It kills worm parasites, in dogs. I think what happened was, a couple of years ago it was accidentally noted that this drug had anti-cancer properties. And it’s actually a really interesting story and a really interesting drug, because the first time I heard about it I thought, “Oh my goodness. Okay, people are taking dog medicines now. What’s going on with this? What kind of crazy stuff is this?”

But that gets an investigation, and it turns out that this drug actually has a feasible mechanism that it could actually have anti-cancer properties. It turns out the way it works is it inhibits microtubules. And microtubules are basically part of the skeleton of cells. They hold the cells together and basically keep them inflated and provide structural support to cells. And of course, cancer cells need that structural support to survive just like normal cells do. This drug inhibits those, and that’s how it kills these worms.

What was happening a couple years ago, they did a study at Johns Hopkins. They had these mice that were completely immunosuppressed. They had no immune system, so these mice would be inoculated with tumors. Because there was no immune system, the tumors would grow easily in the mice, and then the cancer researchers could test various cancer drugs against these tumors.

So were they testing fenbendazole against the tumors? No. Actually, the fenbendazole, because it was an anti-parasitic, was actually being given to the mice in their food.

Jamie DePolo: Oh, interesting.

Dr. Wojciechowski: Yeah, and they noticed that the ones that got the fenbendazole, the tumors wouldn’t grow. So then they started testing, you know, giving some mice fenbendazole, and some mice didn’t get fenbenzadole, and they found that there was a real signal there. The fenbendazole seemed to be helping to kill these tumors in these mice.

Jamie DePolo: Oh, wow. I have a question, too. Now you said it’s a microtubular inhibitor. Does it just inhibit the microtubules in the cancer cells, or does it go out and do things to healthy cells as well? How does it know?

Dr. Wojciechowski: It doesn’t seem to affect the healthy cells as much because cancer cells are growing rapidly, and there’s a lot of turnover with the microtubules. As is the case with just about any cancer drug, it affects tumor cells more so than normal cells because those are the cells that are rapidly dividing and using the microtubules to a greater degree. So, in theory, it should be fairly specific to the cancer cells, but we’re not really sure and I’ll get to that more in a little bit.

Jamie DePolo: So we have this study looking that there’s potential in mice, but there have been a lot of studies with drugs that have potential in mice that don’t pan out in people because of side effects or other things. So is any research on people moving forward because I know there are… I would be nervous about taking a medicine for a dog because I know there are certain medicines that I take, like ibuprofen, that would kill my dog. So I’m assuming that there some of that same problem going back and forth between species.

Dr. Wojciechowski: That’s exactly right, and the bottom line is that we don’t really have any studies in humans, and mice and pinworms are not simply tiny human beings. They are different organisms and, for example, the liver of the mouse may process the drug totally differently than the liver of a human being. And like you said, there’s many drugs that have shown promise in mice but have not really panned out in human beings. I mean, it probably happens every day out there, where in the lab when you have mice and you’re testing drugs on mice and they show promise, and then when they finally make it up to human beings, very, very few of these drugs actually work in humans. The reason is that a human being with cancer is a very different organism than a mouse with no immune system.

Jamie DePolo: Right, right. When I was doing some research on this, I did come across a blog, and there was a man, you may have heard of him, his name is Joe Tippins, and he was diagnosed with metastatic small-cell lung cancer and his prognosis was bad. He had a very poor prognosis.

So according to his blog, his veterinarian told him about these fenbendazole studies and how it was killing cancer cells in mice, and Joe figured he had nothing to lose. He had a poor prognosis. He had metastatic disease. Let’s try it. So he started to take it. He’s still taking it, as far as I understand from his blog, which I just checked last week. He’s taking it as maintenance, and according to his blog he has no evidence of disease.

Now, I can imagine for anyone who’s been diagnosed with metastatic cancer this is a hugely, hugely powerful story. But I guess, as we said, we don’t know the side effects in people. I’m wondering, you know, Joe had small-cell lung cancer, and I’m wondering, is it possible that that particular cancer is possibly more susceptible to fenbendazole than breast cancer?

I ask that because it seems like several, a lot of, most of the new immunotherapies that are coming out seem to work so well in lymphomas and lung cancer, but they don’t really work that well in breast cancer.

Dr. Wojciechowski: Yeah.

Jamie DePolo: So do we know anything about that? If we don’t that’s fine. I’m just curious.

Dr. Wojciechowski: Yeah, so small-cell lung cancer metastatic is a devastating disease, and on average people live only about 9 to 12 months with that particular cancer. But every oncologist has seen a small percentage of people, say maybe 5%, who live up to 5 years with this disease. And there could be a lot of different reasons for that. Even within small-cell lung cancer, everyone is different, and everyone will respond to different treatments in different ways. So one possibility, of course, is that fenbendazole works. Okay? We can’t discount that possibility. The other possibility is that the other chemo drugs that he was on, which also have antimicrotubular activities — for example, Taxol, which has antimicrotubular activities just like fenbendazole, so if he was on that drug you have to ask, maybe it was the Taxol that did it, which has similar properties. It’s hard to know for sure. I’m not his doctor, and I don’t know the details of his case, but my patients ask me about these sort of things all the time. And I’m not going to stand in anyone’s way. I’m not going to say you can’t take X, Y, or Z medication. But on the other hand, people ask me for my advice based on my experience and expertise. And when patients ask me about these things, it usually goes something like this: Well, it hasn’t been studied in human beings, so we don’t know if it helps. But it’s almost as important that we don’t know if it’s harmful either. I would never want to recommend to my patients anything that I was uncertain about, especially when there are other medicines and treatments which do have good studies and we do have a lot of good data and information as to whether or not it helps and what the side effects are.

Jamie DePolo: Okay. Now are any of your patients that you know of taking fenbendazole?

Dr. Wojciechowski: No, not that I’m aware of.

Jamie DePolo: Okay. Because I guess I was just wondering, too, and we probably don’t know the answers to these, like can you take too much of it? I mean, there’s really not a human dose. I know what the dose is for a 50-pound dog. And I guess the other thing, too, that I wonder is what are the interactions with something else someone might be taking?

Dr. Wojciechowski: We have no idea. That’s the problem. We have no idea, and the first principle in medical ethics is do no harm.

Jamie DePolo: Right.

Dr. Wojciechowski: So as a physician, I’m going to want to really be able to understand what the potential side effects are for my patients. So I’m not likely to recommend this drug for my patients right now even though it is a very interesting drug with a mechanism of action that could have some potential. And it’s not unheard of to discover chemo drugs or other drugs sort of serendipitously, or by accident in this manner. Cisplatin is one of the most important chemotherapy drugs, and that was discovered accidentally when a scientist was studying the effects of electric fields on cell division. He found out that when he turned on the electric field the cells stopped dividing. But the electrodes were made from platinum, and it turned out that it wasn’t the electric field that was causing the cells to stop dividing, it was actually the platinum that was being released into the solution. So yeah, I mean it certainly is a very interesting drug with an interesting and maybe even feasible mechanism of action. But until we have the studies in human beings and we know if it really works or if it’s safe, I just can’t recommend it.

Jamie DePolo: Okay, okay. Thank you for that. I’m wondering, too, do you know of any studies that may be looking at fenbendazole and cancer in people? Are people talking about it or considering it, do you know?

Dr. Wojciechowski: I don’t know of any studies that are looking at that specifically right now.

Jamie DePolo: Okay, okay. So in your opinion — I don’t want to put words in your mouth — but it sounds like you are not recommending this to your patients right now, and it’s really kind of a we need to wait and get more information.

Dr. Wojciechowski: That’s correct. And the other thing is we do have chemo drugs that are out now that target the microtubules just as fenbendazole seems to do. So if a patient asked me about it I would probably go in that direction.

Jamie DePolo: Okay. Thank you very much Dr. Wojo. We really appreciate your insights on this. This is going to be very helpful.

Dr. Wojciechowski: You’re welcome, Jamie. It’s been a pleasure.

Thank you for listening to the podcast. Please subscribe on iTunes or wherever you listen to podcasts. To share your thoughts about this or any episode, email us at, or leave feedback on the podcast episode landing page on our website. And remember, you can find a lot more information about breast cancer at, and you can connect with thousands of people affected by breast cancer by joining our online community.

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