Vet School 101 The FDA approves veterinary medicine’s first cancer fighting drug...

...and it’s for the ubiquitous mast cell tumor. Seen primarily in dogs, this common skin tumor has plagued us veterinarians for eons, it seems. Not only can it be a killer, it’s sometimes hard to identify when it masks itself, chameleon-like, as a wart or tiny bump on the skin. (Who can see with all that hair?)

To add insult to injury, it’s exceedingly difficult to arrive at a decision as to whether the tumor you’ve just removed has been cured by your surgery...or whether it’s just going to come back bigger and badder than ever (usually in the same location but sometimes in a local lymph node or internal organ).

Apart from surgically removing a wide swath of skin, fat, muscle (and sometimes bone!) from around the mass (at least one centimeter in all directions but for higher grades, as much as three centimeters), treatment can also include radiation therapy or chemotherapy.

Radiation is especially helpful should the tumor be diagnosed as a high grade malignancy (mast cell tumors are graded on a scale of I-III, III being the worst)...or should it appear in an area where a complete surgical excision is impossible (as on the face or a lower limb). Chemotherapy is indicated for some high grade tumors (Grade III), some incompletely resectable tumors or when metastatic disease (spreading to local lymph nodes, for example) is present.

The trials and tribulations of mast cell cancer is frustrating for veterinarians and confusing for pet owners. That’s especially true when your oncologist disagrees with your general practitioner who also disagrees with your internist. Yes, even among specialists mast cell cancer is hotly debated and subject to many internal disagreements––particularly with respect to the right way to treat them.

The various grades of mast cell tumors and the many modalities we can apply to treat them makes for a perfect storm of confusion. Add that to the tumor’s ubiquity (it’s the second most common tumor type in dogs), and you can begin to understand why mast cell tumors give veterinarians headaches and sleepless nights.

Take, for example, one of my recent MCT patients. She was diagnosed with a Grade II, but margins were “dirty” (not completely free of tumor). One oncologist wanted to irradiate immediately. Another general practitioner suggested injecting the area with prednisolone (a steroid) and a surgeon wanted me simply to go back and get clean margins. A radiation oncologist at the University of Florida finally ratified the surgeon’s opinion, discrediting the injections and stating that radiation was unnecessary for a surgically resectable Grade II. So you know, I ultimately went with the latter, well-informed approach. But what a mission!

That’s why the news of a new cancer therapy specifically for mast cell cancer is both exciting and stressful. Hooray for my more severely affected patients with recurrent disease! But what’s that going to mean for my recommendations? It’s no stretch to say that I’m a tad confused––as seems to be the case with some of my colleagues on VIN (the Veterinary Information Network), too.

So I did some research. This drug is called Palladia. Manufactured and marketed by Pfizer, the drug (oral) is in a class of drugs called tyrosine kinase inhibitors. They work by blocking the activity of receptors important for the development of blood vessels supplying the tumors, as well as for receptors critical to tumor survival. Its stated use is for canine mast cell tumors that recur after surgical excision, with or without local lymph node involvement. It shrinks these tumors and extends the comfortable life of these patients.

Side effects? I don’t have the percentages, but many dogs apparently experience gastrointestinal symptoms like vomiting, diarrhea and inappetance. Lameness, too. They appear to be reversible. Death is possible, however––though very rarely with careful attention to side effects.

The other side effect worth considering is the price. A similar drug marketed by Pfizer for humans, Sutent, goes for $5,000 (for 28 pills!). Who knows what Palladia will cost, but it's safe to assume it won't be that expensive. Nonetheless, I bet its price will best radiation's priciness but come in well over what standard surgical techniques would cost.

For now, Palladia will only be in the hands of oncologists and internists (as Pfizer decides how it’s going to market the drug and accumulates more data through this select group of professionals). But the common nature of this tumor likely means that Palladia will be coming to a veterinary hospital near you. I guess then it’ll come time to implement the new drug. As it stands, I’m not so sure its benefits outweigh the risk of its side effects when you consider that another surgical resection might be just as curative (if there’s no evidence of metastasis)––statistically speaking, anyway.

Yes, it’s clear that lots of confusion still reigns. But one thing I do know is this:

It’s about time veterinary medicine had a drug FDA-approved for use against cancer. This is where oncology is headed––away from invasive surgery, stressful radiation and indiscriminate chemotherapy...and more towards vaccines (like the melanoma vax), gene therapy––and, of course, drugs like this one.

June 5th, 2009

Add Comment18 Comments

Exciting news!

My aunt lost her 8 y/o cat following unsuccessful MCT surgery two years ago, and I know a really neat dog who had to have much of his tail amputated last year to remove a large MCT... those things are nasty.

Ramen Connoisseur June 5th, 2009 11:37:33 AM

Thanks for posting this, and for doing your homework! Much more info than the Yahoo News announcement a member posted in the Tripawds canine cancer discussion forums. Big Surprise. ;-)

tripawds.com June 5th, 2009 02:00:56 PM

I have a rescue that had a mass removed from her hip. We were using an inexpensive (i.e. "cheap") vet at the time. They removed a mass which they knew we wanted sent out for a pathology report. They did not take enough tissue, when it came back as a MCT, the dog had to undergo another surgery. She also had various lumps and bumps removed at that time. Happily the second surgery went well, she has stayed cancer-free for a year and a half. All we can do is take it one step at a time, and she has stayed with me as a forever foster due to her health.

At the time, every vet we talked to had a different idea of how to handle a MCT. It would be nice to have a set protocol. But $5000 for meds? No not likely, but even $500? Hmmm. That would be a big bite.

robinsdogs June 5th, 2009 04:22:15 PM

robinsdogs: The ideal approach to any mass is to aspirate it first, put it on a slide, stain it and look under a microscope. Mast cell tumors are easy to diagnose this way (though you won't know the grade until you actually remove the mass) and this way you know you have to take a wide approach around the tumor (unlike our approach for other skin masses). It makes it easier (though by no means foolproof) to get clean margins.

The problem with MCT is that many of them send tendrils of cancer tissue deeply into the skin (and sometimes fat and muscle) surrounding the mass. That means that even wide excisions might not get it all and you get "dirty" margins. A follow-up surgery is always indicated in these cases (unless there's no room left in the area to excise more, in which case you go for radiation and sometimes even chemotherapy).

Hope this helps. But, yes, every veterinarian seems to think something different about MCTs. Yet there are some set ways to go about things. Problem is, these set things are always changing according to new research (and there's a lot going on). Frustrating, right? Nonetheless, it's great that we're evolving. It's just that it takes time for everyone to get on board with the newest protocols. Luckily I have specialists around me (and I buy them lunch a lot) so I can always ask the best and the brightest when I don't have time to digest everything in the journals. ;-)

Dr. Patty Khuly June 6th, 2009 05:35:20 AM

My male lab Chauncy had a MCT removed from his upper lip 18 months ago. It literally appeared overnight. We weren't sure how much lip he was going to loose but all I wanted was clean margins. The night before the surgery I found another similiar looking lump in his armpit that literally was not there the 3 days before. My vet and I had gone over every inch of him twice in the week before his surgery. I had the second lump removed rather than wait for a biopsy since we already were doing surgery. That one turned out to be a histiocytoma. My vet got clean margins and Chauncy has not had a recurrrance.

The best part of this news is that it means to me that we will be seeing more drugs in the future to properly treat other cancers specifically tailored for our animals.

Elizabeth - from Nova Scotia June 6th, 2009 08:30:36 AM

My mixed lab had a grade II mast cell tumor removed from his neck with clean margins according to the pathology report. I believe it had been about 17 months when I felt a small swelling within his neck. It was a lymph node. This was in 2007 and I ordered and read 33 veterinary journal articles pertaining to mast cell cancer. I certainly understand your frustration because at the end of my reading I was absolutely distraught. Each finding in a particular study was contradicted by the conclusions of another. I felt no better prepared to make decisions than when I started. Anyway, off we went to the oncologist with all this rolling around in my head. According to the oncologist surgery would be useless. Radiation was not well advised because he did not do well at all away from me. My opinion of the chemo suggested, which might do something or nothing to gain time, was that it amounted to torturing an old dog until he died, and I stated such. The reply was: "Just because we can do something doesn't mean that we should." Because of my experience with this cancer I read the FOI summary for Palladia. I expected it to not be pretty, and it wasn't. Out of 145 dogs in the clinical trial, there were five deaths possibly drug related. They relayed a percentage rate of response, but how long did these dogs LIVE? How much time did they gain and what was their quality of life? That is the bottom line to me. I suppose we will have to wait to see what the future brings for those answers. As to my dog, we put him on prednisone, benadryl, and a stomach protectant, and he was put to sleep between 5 and 6 months later. I can't say what I would have done had this drug been available to add to the agonizing decision mix.

BJ Thurman June 8th, 2009 11:19:25 PM

BJ Thurman: Your story sounds so familiar. How sad. I'm hoping your case is one where we'll be able to implement this therapy.

Dr. Patty Khuly June 9th, 2009 08:05:26 AM

Have vets tried lowdosenaltrexone.org therapy on cancers or autoimmune disorders? Apparently it stimulates the immune system. It should be very cheap and worth a try.

Pat Herrmann

Patricia Herrmann June 9th, 2009 08:52:31 PM

My small mixed breed dog (10 lbs) developed a MC tumor. She was treated at Florida Veterinary Specialists in Tampa, FL. It was inoperable - on her leg. She completed the prescribed course of radiation and chemo. Neither stopped the growth. She was then put on a "study" medication which consisted of a small pill every day. She went in to remission 3 months later and has been cancer free for almost 3 years. This study medication comes from Paris France and she will continue to take one small pill per day for her lifetime

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