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Vaccines and tumors in cats

Very rarely, a cat will develop an aggressive cancerous tumor called a sarcoma at the site of an injection. Dr. Lee discusses questions to ask your vet about the types of vaccines being used.

Vaccines and tumors in cats

Q: When I mentioned to a friend that I usually have my cats vaccinated for rabies at a vaccine clinic, she told me that the inexpensive vaccines used at vaccine clinics can cause cancer. She recommended I have my cats vaccinated by a veterinarian who would use a vaccine that doesn’t cause cancer. Can you explain?

A: Very rarely, a cat will develop an aggressive cancerous tumor called a sarcoma at the site of an injection. Any injection, from an antibiotic to a steroid, can induce an injection site sarcoma (ISS). However, large epidemiologic studies show that ISS occurs in fewer than one of every 10,000 vaccinations.

The risk may be higher with vaccines that contain adjuvant, an ingredient that strengthens the cat’s immune response. Rabies vaccines with adjuvant are generally less expensive than vaccines without it, since more expensive technology is required for the vaccine to stimulate the immune system without adjuvant.

Although the risk of ISS is extremely low, most veterinary experts recommend vaccinating cats with non-adjuvanted vaccines. Fortunately, non-adjuvanted rabies vaccines are now available with both one- and three-year durations.

Ask the vaccine clinic if they use a non-adjuvanted rabies vaccine, and ask your regular veterinarian for guidance about your cats’ vaccinations.

Lee Pickett, V.M.D. practices companion animal medicine. Contact her at

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