pet connection

After hearing what Dr. Laura D. Garrett of the University of Illinois had to say about Palladia at last month’s Western Veterinary Conference, I realized there’s more to the story than the fact that this is the first drug approved in the United States to treat canine cancer.

Palladia (toceranib phosphate) is what’s known as a “tyrosine kinase inhibitor.” That means it blocks an enzyme that can help cancer spread.

Other tyrosine kinase inhibitors (TKIs) include the human drugs Sutent (sunitinib) and Gleevec (imatinib mesylate), and a European veterinary drug, Masivet (masitinib), which will be known as “Kinavet” if it’s approved in the United States.

Right now, Palladia is approved to treat mast cell tumors in dogs, and it’s fairly successful at treating those that don’t respond to other forms of treatment. In one study, mast cell tumors were reduced in size in 43 percent of dogs who received the drug, while only 8 percent of the dogs given placebo responded similarly.

Dr. Garrett, who is a board certified specialist in oncology, cautioned that TKIs are not a first line of treatment, but are meant to be used for particularly severe mast cell disease and only after other forms of treatment, like surgery, radiation and chemotherapy, have failed.

Even then, these drugs don’t always work. But for some mast cell tumors, particularly those with mutations in what’s known as the c-kit gene, TKIs have a much greater chance of success. Your veterinarian can have your dog’s tumor tested to see if it has that mutation.

Another big plus to treating cancer with Palladia is that it can be given at home, unlike other forms of chemotherapy. However, that’s a minus, too, because it can cause pretty severe side effects, mostly gastrointestinal. Owners have to be very vigilant in watching for signs of diarrhea or vomiting, and getting the dog to the veterinarian immediately.

There’s another potential benefit for dogs in the approval of a veterinary TKI: research. Manufacturers of human drugs don’t test them for how well they work in animals, but those making veterinary drugs do. Pfizer and AB Science are continuing to sponsor research into mast cell tumor treatment and other uses of their TKIs, which can lead to better ways to treat many kinds of cancer.

And once a veterinary drug is approved for one use, it can legally be used “off-label” to help animals with other problems. So veterinarians can try TKIs in the hope that they might benefit animals who aren’t responding to other therapies. Their outcomes will contribute to the body of knowledge about this class of cancer drugs, and possibly lead to new research and new and better therapies.

The first FDA-approved veterinary cancer drug isn’t going to cure every case, or even most of them. Neither will other tyrosine kinase inhibitors as they roll out of the pipeline. But cancer is one of the worst enemies a veterinarian ever battles. The more weapons we have against it, the better.

Right now, only boarded specialists who treat cancer have access to the drug, although it’s expected to be available to veterinarians in general practice later this year. If your dog is diagnosed with a mast cell tumor and you want more information on TKIs, talk to your veterinarian and see if he’s likely to be helped by this drug.

Photo courtesy of Pfizer Animal Health.

Disclosures: Palladia is manufactured by Pfizer Animal Health, and Pfizer sponsors the web archive of the Pet Connection syndicated feature.

Dr. Garrett does not work for Pfizer, but received an honorarium for presenting on Palladia at the Western Veterinary Conference. She also received, as did all board certified veterinary specialists who treat cancer, free Palladia for use in her patients during its testing and introduction.