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Pfizer Hits a Home Run with New Canine Cancer Drug

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In a ‘first’ for veterinary medicine, Pfizer Animal Health, a business of the pharmaceutical giant Pfizer, Inc., (ticker symbol: PFE) recently announced that the U.S. Food and Drug Administration (FDA) has approved the first canine cancer therapy in the U.S. The drug -- PALLADIA™ (toceranib phosphate) -- has been developed by Pfizer to treat mast cell tumors (MCT) in dogs.

MCT is the most common skin tumor arising in dogs and the second most common tumor type overall, accounting for 16% of the 1.2 million new canine cancer cases in the U.S., according to Pfizer market research. (The condition also occurs in cats, though much less commonly.) It affects certain breeds more often than others: Boxers, Boston Terriers, Labrador Retrievers, Beagles, and Schnauzers.

While a number of human chemotherapy agents have been used in dogs for many years, all of them were developed for human use. PALLADIA™ is the first drug to be specifically approved for the treatment of canine cancer; it is not approved for use in humans.

Mast cell tumors: the basics

Diagnosing the problem

Mast cells are specialized cells that are normally involved in the process of inflammation, such as allergic responses, tissue growth, and wound healing. Typically, MCT appears as skin swellings or red, itchy lumps that vary in size and general appearance. They may mimic other skin conditions and can only be definitively diagnosed through a biopsy. Other procedures that may be performed to confirm the diagnosis and determine the stage of the disease include x-ray, blood tests, the removal and analysis of lymph nodes, and ultrasound imaging.

The current standard of treatment

Current treatment protocols almost always begin with surgery to remove the main tumor mass and a margin of normal tissue around the tumor to reduce the possibility that any cancerous cells remain (often what is visible on the surface of the skin is only a fraction of the tumor present).

MCT is an invasive form of cancer that may spread to internal organs. For this reason, and because it is not always possible to know for certain that all affected cells have been surgically removed, radiation therapy and/or chemotherapy may be recommended following surgery to reduce the likelihood that the disease will spread. Whether one or more of these additional – or “adjuvant” -- therapies is used will depend on a number of factors:

  • The Grade -- or degree of aggressiveness -- of the tumor; tumors are classified as Grade I, II, or III.
  • Whether the veterinarian was able to remove the entire tumor mass surgically, leaving clean, i.e. cancer-free, margins
  • Whether the disease has spread to adjacent lymph nodes or to internal organs

Karen Oberthaler, VMD, ACVIM, a board-certified veterinary oncologist with NYC Veterinary Specialists, explains: “In the case of Grade I tumors that are completely excised surgically, you’re done, and the cancer is usually cured without the need for further treatment. For Grade II tumors where the disease has spread beyond the original site, we consider following up with chemotherapy. With Grade II tumors where the disease has been cleanly resected, we will often irradiate the scar. With Grade III tumors, more intensive treatment is appropriate.”

The science behind Palladia™

Amy Trettien, DVM, Pfizer’s Senior Manager for Veterinary Operations, explains that Palladia™ targets certain types of tyrosine kinase (TK) receptors. TK receptors are found on cells throughout the body.  It has been shown that changes in certain TK receptors are associated with some types of cancer in humans and in dogs.

Two of those receptors – designated “PDGFR” and “VEGFR”, are associated with the formation of the blood vessels that the cells need to grow, a process called “angiogenesis.”  A third -- called “KIT” -- when mutated or over expressed, can contribute to uncontrolled cellular proliferation.”  By blocking all three of these receptors, Palladia™ packs a one-two punch, attacking the cancer cells directly while also depriving them of their blood supply.

Cheryl London, DVM, PhD, a veterinary oncologist and Associate Professor at The Ohio State University College of Veterinary Medicine was one of the principal researchers in the development of Palladia™.  In a recent interview with WebVet, Dr. London explained that Palladia™ represents the fruit of research that began in 2000 with a search for agents that would inhibit the KIT receptor.

Although Palladia™ is approved only for the treatment of MCT, Dr. London anticipates that researchers will soon be looking into the use of the drug in the treatment of other canine cancers, such as certain sarcomas and carcinomas.

Palladia™ changes the landscape

In a News Release announcing its approval of Palladia™, the FDA described the drug as “an important step forward for veterinary medicine,” pointing out that “prior to this approval, veterinarians had to rely on human oncology drugs, without knowledge of how safe or effective they would be for dogs. Today’s approval offers dog owners, in consultation with their veterinarian, an option for treatment of their dog’s cancer.”

Oberthaler, Trettien, and London agree, however, that Palladia™ is not intended to replace other therapies, but to complement them. Surgical removal of the tumor mass(es) will remain the initial treatment of choice for MCT in most cases. Trettien calls it “another tool in the toolbox” and predicts that Palladia™ will be “part of a multi-modal protocol that will be used in combination with other treatments.”

While the research studies thus far have only involved the use of Palladia™ in dogs with late-stage MCT, all three veterinarians agree that as experience with the drug grows, it may turn out to be effective in earlier stages of the disease as well. Only time -- and further research -- will tell.

Responsible product introduction

Although the potential market for the drug is modest given the incidence of MCT, for an initial six-month period, Pfizer will make the drug available only to board-certified veterinary oncologists, internists, and dermatologists.

The goal is to provide veterinary specialists with Palladia clinical experience and gather additional information on how Palladia™ can be used in conjunction with treatments already in use in order to produce the best possible outcomes for patients.  

Introducing Palladia™ to the veterinary community this way is part of Pfizer’s policy of responsible product introduction.  Trettien explains: “It is advantageous for our veterinary patients to make a product available after the specialists that set treatment protocols have had clinical experience with the product in a real-world setting.”

With more than 1,500 such specialists around the country, most affected dog owners will be able to find one within a reasonable distance of home.

So, if my dog has MCT?

If you are the owner of a dog with MCT, seek the advice of a veterinarian. Grade I MCT is usually curable by surgery alone. If your dog has a higher grade tumor, especially one that has spread beyond its original site, your veterinarian may recommend referral to a veterinary specialist and additional treatment, including PALLADIA™, may be considered.

Although Palladia™ will not replace other treatments for MCT, it is clearly a major step forward in canine cancer treatment, but as with the treatment of any serious pet illness, consider all the options and make your decision an informed one.

 

 

Credit: Reviewed by Amy Attas, DVM
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