Vaccines and Sarcomas: A Concern for Cats

Those of us entrusted with caring for cats have two basic desires: first, we wish to help cats by preventing serious diseases and death; second, we wish to keep them from harm. Achieving both objectives at the same time seems simple enough. Unfortunately, few medical procedures are totally without risk, and sometimes procedures that are normally helpful can cause harm. The association between vaccine administration and sarcomas (specific kinds of cancer) is an example.

Is this something new?
Sarcomas are not new forms of cancer in cats. But in 1991, veterinarians began to notice a higher than expected number of sarcomas occurring on cats’ bodies in places where vaccines are commonly injected. Subsequently, an association between vaccine administration and sarcoma development has been established. Most feline sarcomas are not linked with vaccines in any way-and those that are associated occur infrequently-yet veterinarians are deeply concerned.

I found a lump where my cat was vaccinated. What happens now?
It is quite common for a small, firm, painless swelling to form under the skin at the site where a vaccine was injected. The lump is almost always of no consequence and disappears after several weeks. Rarely, however, the swelling may progress to a sarcoma. To be on the safe side, your veterinarian will suggest that you periodically check the vaccination area for several months after vaccination. If you detect a lump, you should contact your veterinarian as soon as possible. Small samples of the lump will be sent to a laboratory for diagnosis if any of the following are true:

 The lump persists for more than three months after vaccination.
 It is larger than two centimeters in diameter (about the size of an olive).
 It is increasing in size one month after vaccination.

If the lump is found to be a sarcoma, your veterinarian may confer with or refer you to a veterinary oncologist (a cancer specialist) for management.

If vaccines are causing problems, why use them at all?
Disturbing as this issue may be, there is great concern that cat owners, attempting to keep their cats from harm, may forego vaccination entirely. The result? Though well intentioned, these owners may be placing their cats at far greater risk of acquiring a fatal infection than any risk the vaccine poses. And in the case of rabies, human health is at risk as well.

So what’s being done?
Even though vaccine-associated sarcomas are uncommon, the problem is receiving unprecedented attention by veterinarians and feline vaccine producers. The Vaccine-Associated Feline Sarcoma Task Force is a coalition of national veterinary organizations dedicated to resolving the dilemma. This group is devoting considerable human and financial resources to determine the true scope of the problem, the cause, and the most effective treatment of vaccine-associated sarcomas.

How should I respond?
Until this problem is solved, the best response is to discuss the issue with your veterinarian. In the vast majority of situations, vaccines are much more beneficial than harmful, and they continue to help protect cats from serious infection and disease. But one way to reduce the chance of sarcoma development is to not vaccinate unnecessarily. Veterinarians are being urged to evaluate each individual cat’s risk of infection to guide in deciding which vaccines should be given. After considering both the vaccine and your cat’s situation, your veterinarian will assist you in designing a vaccination program that not only protects against infectious disease but also is as safe as possible.


Reprinted with permision from the Cornell Feline Health Center, 607-253-3414;