Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Scared of a Shot? The Risk of Vaccine-Associated Sarcomas in Cats

Pet Column for the week of February 15, 2010

Related information:

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ashley Mitek
Information Specialist

Source - Jacqueline M. Wypij, DVM, DACVIM (Oncology)
In the early 1990s a few veterinarians started to notice a disturbing trend. Sarcomas, a type of malignant tumor, were being found more frequently in cats. The location of these masses was quite suspicious--they were in the same area in which routine vaccinations were administered.

Shortly thereafter, experts came to the startling conclusion that the feline leukemia vaccine and the feline rabies vaccine may be to blame, (although other causes have since been identified as well). Because of this development, the Vaccine-Associated Feline Sarcoma Task Force was established in 1996 by several prominent organizations, including the American Veterinary Medical Association.

The swift and massive response likely had to do with the fact that sarcomas are a difficult type of tumor to treat. Surgical excision of the mass (requiring general anesthesia) with wide margins is necessary in nearly all cases. In addition, the tumors almost always recur and appear to have a higher rate of metastasis (spread) to other parts of the body.

So the question arises, do the benefits of vaccinating your cat for these diseases outweigh the risks?


"The risk of getting an infectious disease is much higher than the risk of developing a sarcoma at the injection site," explains Dr. Jackie Wypij, a veterinary oncologist at the University of Illinois Veterinary Teaching Hospital in Urbana. Current statistics estimate that 1 in 5,000 to 1 in 10,000 cats receiving a vaccine will develop a sarcoma.

Since the task force began studying the problem, there has been much reform. For example, new vaccination schedules have been developed, decreasing the frequency in which the shots need to be administered and specifying specific anatomic places to inject them. In addition, because the aluminum adjuvants (a chemical agent used to stimulate an immune response) in the vaccinations were suspected to cause the problem, vaccine manufacturers have ceased using them.

Still, it is important to weigh the risks. For example, an older indoor cat may not need the feline leukemia virus vaccine. Except that, if that cat escapes out of the front door one day when you're not looking, you may be asking for trouble. All it would take is for your unvaccinated indoor cat to come into contact with a leukemia positive cat, and presto--your beloved Fluffy may have feline leukemia. Although the diseases is not one that is transmitted easily, it nevertheless is a terminal disease that could have been prevented.

In the case of rabies, there is not much leeway. In many municipalities the vaccine is required for cats and dogs. Not doing so may be breaking the law, and also puts your pets' welfare in limbo if it bites a human. Let's say your unvaccinated cat bites your child's playmate one day when they are playing a little too rough. Without proof of a rabies vaccination, animal control officials can seize the animal from your house and quarantine it. It's also worth noting that the only definitive way to test for Rabies is with a brain biopsy.

In the end, vaccine-associated sarcomas are still a hot topic in veterinary medicine. The risks of vaccination should not be overlooked, but neither should the potential benefits. To decide what is best for your cat, please talk to your local veterinarian.