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Palladia: New Treatment for Mast Cell Tumors

Not without risks, but a good option for inoperable tumors in particular.

News item written by Mary Straus, published in the Whole Dog Journal, August 2009

In June 2009, the FDA approved the first drug used specifically to treat cancer in dogs. The new drug, called Palladia (toceranib phosphate) and made by Pfizer Animal Health, targets mast cell tumors. It does not replace surgical removal, but is used for higher-grade tumors that recur after surgery, with or without lymph node involvement. It is not recommended for dogs with systemic mast cell tumor, due to the increased risk of adverse side effects.

Mast cell tumors primarily affect the skin. They can vary widely in appearance and must be identified by fine needle aspirate or biopsy; there’s no way to tell if a lump or bump is a tumor by looking at it or feeling it. Mast cell tumors are graded on a scale of I to III, with III being the worst. They are the second most common tumor found in dogs. If left untreated, they can spread to other parts of the body.

Surgical removal with wide margins is always the preferred treatment for this type of tumor, but that’s not always possible, particularly when the tumor is in an area without a lot of extra skin, such as the face or lower limbs. Chemotherapy and/or radiation therapy are used in these cases, as well as for high-grade tumors and those that have spread.

Palladia is a tyrosine kinase inhibitor that works by killing tumor cells and cutting off the tumor’s blood supply. The result is that it shrinks the tumors and prolongs survival time. The initial study of 86 dogs found the tumor disappeared in 8.1 percent of treated dogs, shrank in 29.1 percent of dogs, and stopped growing in another 20.9 percent of dogs. In addition, Pfizer reported that quality of life improved in dogs whose tumors responded to treatment.

In its testing phase, Palladia was found to cause side effects in the majority of dogs who received it; these included diarrhea, decrease of loss of appetite, lameness, weight loss, and blood in the stool. Additional side effects were reported in a minority of the dogs. Most side effects are mild and resolve when the drug is stopped temporarily and then dosage is reduced, but in rare cases they can be life-threatening.

Palladia is given continuously every other day, with weekly vet checks and blood work recommended for the first six weeks, then every six weeks thereafter. The cost is as yet unknown, but it’s likely to be expensive, especially when the cost of follow-up care is included. For these reasons, if there is no lymph node involvement and it’s possible to try again to surgically remove the tumor after it recurs, that could be the better choice. You’ll need to discuss all treatment options with your vet before making a decision.

Palladia will be available in 2010. Initially, it will be available only to oncologists and internal medicine specialists.

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