The threat of a rare but serious condition in cats -- vaccine-associated feline sarcoma -- is prompting veterinary experts to advise cat owners and their veterinarians to think twice about whether all vaccinations are necessary for all cats.

"More so now than ever, the individual cat's environment and risk of exposure should determine whether particular vaccines are administered," said James R. Richards, D.V.M. Richards is director of the Feline Health Center at the Cornell University College of Veterinary Medicine, as well as chair for education and communication at the national Vaccine-Associated Feline Sarcoma Task Force.

The 10-member task force is made up of representatives from the American Veterinary Medical Association, American Animal Hospital Association, Veterinary Cancer Society, American Association of Feline Practitioners, U.S. Department of Agriculture, Animal Health Institute and the Cornell Feline Health Center.

Vaccine-associated feline sarcoma is the name that veterinary scientists give to the

higher-than-expected number of cancerous tumors developing where cats have been vaccinated. Veterinarians began noticing sarcomas at vaccination sites on cats' bodies in 1991, and since that time research has shed some light on the issue. (See attached: "Vaccines and Sarcomas: A Concern for Cat Owners.")

"Even though the problem seems to be quite uncommon -- in the range of one to four per 10,000 vaccinations -- the tumors themselves are quite serious and are very difficult to manage successfully," Richards said. "These are progressive tumors that continue to grow unless they are surgically removed -- and sometimes even after they are removed."

The sarcomas are most frequently associated with vaccinations against feline leukemia virus (FeLV) and, to a lesser extent, against rabies virus, the cat doctor observed.

Research is being conducted in the hope of answering several questions. Among them: How common is the condition among the approximately 60 million pet cats in the United States? What is the cause? What is the best way to treat the tumors? What is the outlook for affected cats? And, should vaccination protocols be changed? The American Association of Feline Practitioners is expected to release new vaccination recommendations this summer.

In the meantime, both cat owners and veterinarians should review the need for vaccinations on a case-by-case basis, the Cornell Feline Health Center and the sarcoma task force recommend. A low risk of contracting certain diseases may not warrant vaccination, the experts now suggest.

"For example, if we have a cat that spends time outside, then that animal presents a different risk of feline leukemia, compared to a cat that stays exclusively indoors and is never around cats that go outdoors. It may be appropriate to omit the feline leukemia vaccination for an indoor cat. These are the considerations that cat owners and veterinarians should discuss," Richards said, noting that rabies vaccinations are required by law in some U.S. locations, regardless of where cats spend their time, and one "shot" will always be appropriate.

"We feel that the standard three-way vaccine [against panleukopenia, calici virus and rhinotracheitis] is something that every cat should receive," Richards said. Skipping vaccinations altogether would not be wise, because that could place cats at greater risk of life-threatening illnesses, he said. "The benefits of vaccination still outweigh the risks in the vast majority of situations. But when we find a situation where we can omit a vaccination, that's what we want to do."

Vaccines and Sarcomas: A Concern for Cat Owners

Feline Health Center
College of Veterinary Medicine
Cornell University

Those of us entrusted with caring for cats have two basic desires: First, we wish to help cats by preventing serious disease and death; second, we wish to do them no 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 possible association between certain vaccines and sarcomas (specific kinds of cancer) is an example.

Is this something new?

Sarcomas are not new, nor are they extremely rare. But in 1991, veterinarians began to notice a higher-than-expected number of sarcomas occurring on the body in places where vaccines are commonly injected. Since most sarcomas are not linked with vaccines in any way -- and those that are associated occur only infrequently -- it is very difficult to establish a clear relationship. Veterinary scientists are clarifying the picture, but much more needs to be learned.

So what's being done?

Veterinarians are deeply concerned. 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 concerned 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 exact cause and the most effective treatment of vaccine-associated sarcomas.

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 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.

What should I look for?

It is quite common for a small, firm, painless swelling to form under the skin at the site where a vaccine was injected. The swelling is almost always of no consequence, and it usually disappears after several weeks. Rarely, however, the swelling may progress to a sarcoma, so it's important that you contact your veterinarian if you notice a swelling at the vaccine site. In fact, it's wise to contact your veterinarian if you suspect an adverse reaction of any kind after vaccination.

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. They continue to do an excellent job of protecting cats from serious infection and disease. But one way to reduce the chance of tumor 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 designinga vaccination program that not only protects against infectious disease but is as safe as possible.