In 1991 veterinary medicine suffered a disturbing revelation. Two commonly used feline vaccines were linked to the development of malignant tumors at the site of vaccination. The tumors, called fibrosarcomas, are associated with the vaccines for rabies (in cats only) and feline leukemia. They are aggressive and difficult to remove. They occur in approximately one out of every 3000 – 10,000 cats who receives a rabies or leukemia vaccine.

The discovery of these so-called vaccine associated fibrosarcomas lead to the creation of a special task force (called, unsurprisingly, the Vaccine Associated Fibrosarcoma Task Force). The recommendations of the task force were supposed to cause a dramatic shift in the way cats are vaccinated.

Prior to the discovery of the fibrosarcomas and the formation of the task force, most cats were vaccinated against rabies and leukemia every year. The vaccines were administered between the shoulder blades because that is the easiest place to give injections to cats.

The task force recommended that the leukemia vaccine should be administered only to cats who spend time outdoors. The rabies vaccine should be administered as required by law. If possible, both vaccines should be administered no more frequently than once every three years.

Finally, the task force advised veterinarians to change injection sites. Fibrosarcomas between the shoulders are virtually impossible to remove. Therefore, the leukemia vaccine should be administered in the left rear leg, near the ankle. The rabies vaccine should be administered similarly in the right rear leg. If a fibrosarcoma develops in either of these locations, the cat’s life can be saved by amputating the leg–a less than perfect solution to the problem, but better than the alternative.

Vaccine associated fibrosarcomas are a source of angst for me. I have worked during my career to minimize the number of rabies and leukemia vaccines I give to cats. And I always give the vaccines in the rear legs.

However, a very disturbing paper published in the February 1, 2009 Journal of the American Veterinary Medical Association (JAVMA) indicates that many veterinarians are ignoring the recommendations of the task force and needlessly endangering the lives of their feline patients. According to the paper, significant numbers of cats are developing vaccine associated fibrosarcomas between their shoulder blades. This means that significant numbers of veterinarians are still giving rabies and leukemia vaccines in that spot.

Here are the conclusions of the paper.

Conclusions and Clinical Relevance–Despite publication of the vaccination recommendations, a high proportion of tumors still developed in the [region between the shoulder blades] . . . [v]eterinarians are complying with vaccination recommendations to some extent, but need to focus on administering vaccines as [far down] as possible on a limb to allow for compete surgical margins if amputation of a limb is required. (J Am Vet Med Assoc 2009;234:376-380)

What can you do to ensure that your vet is following the task force’s recommendations? Talk to him or her. Ask whether vaccination for leukemia and rabies is appropriate for your cat. If the vaccines are appropriate, ask where they will be administered. Never accept a one-size-fits-all approach to vaccination.

Photo: A vaccine associated fibrosarcoma between the shoulder blades of a cat, courtesy of Texas A&M’s School of Veterinary Medicine.