Many years ago, when I started my career in veterinary medicine as a veterinary technician, I remember being puzzled as to why we vaccinated cats in so many locations on their bodies.

The rabies vaccine was given in one leg, while the feline leukemia vaccine was given in another leg, and the panleukopenia vaccine was given in yet another leg. When I was brave enough to ask why we vaccinated cats this way, I was given my first taste of veterinary oncology. It turns out that in about 1 out of every 10,000 cats, vaccines can cause something called vaccine-associated sarcomas.

The notion that a vaccine can cause a type of tumor is scary for cat owners. However, over the past 10 to 20 years, there has been a lot of effort by the veterinary community to decrease this risk. Special task forces have been developed to determine the best location to vaccinate your cat, how often to vaccinate, and the safest vaccine.

You may have noticed that your veterinarian used to vaccinate your cat between the shoulder blades and now they do it on a leg or on the tail. This practice was developed to make it easier to treat a tumor if it occurred. Some vaccines are administered every year, while others can be administered every three years to decrease the risk of developing a sarcoma. Vaccines, such as feline leukemia virus, may only be given to your cat if your veterinarian feels your pet is at an increased risk of catching this virus.

Vaccine-associated sarcomas can develop over weeks to years after a vaccine is administered. These tumors are thought to occur from inflammation incited by the vaccine that causes these cells to divide. The best results for tumor control occur when aggressive surgery and radiation therapy are combined. Cats that undergo this type of treatment can be tumor-free for approximately two years. It is recommended that the tumor be removed by a board-certified surgeon because these can be extremely difficult to remove completely.

If the tumor was not completely removed or if you cannot pursue surgery and radiation therapy, there are other treatment options. Injectable chemotherapy may help prevent the tumor from growing back if it was not completely removed. Palladia, a medication approved for the treatment of mast cell tumors in dogs, is being investigated for use against vaccine-associated sarcomas in cats. Preliminary results show that Palladia may slow the growth of this tumor in cats.

The risk of developing a tumor from a vaccine may be much less than your cat catching a deadly virus that could have been prevented with a vaccine. In fact, the rabies vaccine is required by law for all dogs and cats. Please discuss your cat's vaccine needs with your regular veterinarian. It is also important to alert your veterinarian to any masses you may feel when petting your cat at home.

[ Karri Miller works at Veterinary Healthcare Associates in Winter Haven. She is the only full-time board certified veterinary oncologist in Central Florida. Send questions to at petcancerdoctor@gmail.com. ]

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