Also known as injection site sarcoma, this cancer is thought to affect between one and three cats out of every 10,000 cats vaccinated. Some vets believe the incidence is much higher, as much as one cat in every thousand.
These odds may be low, but for most cat owners, the numbers are high enough to cause concern.
What Is Vaccine Associated Sarcoma?
A sarcoma is a malignant tumor that grows in the body's connective tissue. This type of tumor can grow very quickly, and can metastasize to other parts of your cat's body. An injection site tumor is thought to be caused by the cat's immune system reacting to the vaccine.
Surgery to remove this type of tumor isn't always effective, as microscopic tendrils reach from the sarcoma into the healthy tissue surrounding it. These tendrils remain after surgery and can cause the tumor to regrow, often within a few months. In fact, 62 percent of vaccine associated sarcomas will grow back within six months.
Most cats who develop VAS are between seven and nine years old. These tumors can develop within weeks of a rabies or feline leukemia vaccination, but may take years to show up.
Is Vaccine Associated Sarcoma A New Disease?
VAS was first seen in the late 1980's when vaccine manufacturers started using aluminum as an adjuvant to boost the body's immune response to the vaccine. Vaccines containing adjuvants have been implicated in the development of injection site sarcomas.
Should I Continue To Vaccinate My Cat?
Rabies vaccination are required by law, so it's hard to get around them. However, The American Association of Feline Practitioners has suggested vaccinating cats for rabies every three years instead of every year. There is also evidence that older cats don't need yearly boosters since immunity developed from kitten shots probably lasts as long as the cat lives.
What You Need To Do
If your cat is sick, or has an immune system problem, or has had a vaccine reaction in the past, he should not be vaccinated.
Is your cat at risk for the disease the vaccination is supposed to prevent? Every vaccination may not be necessary for every cat.
Use only vaccines that do not contain adjuvants.
Ask your vet about the side effects of every vaccine, including allergic reactions or VAS.
Do not allow your cat to be vaccinated in his "scruff," or the loose skin on the back of his neck. If he should develop VAS, it's very difficult to treat in this area because it's so close to his heart and lungs. Instead ask that he receive the shot in his back leg, where VAS is easier to treat, should it develop in the future.
Your vet should record the vaccine manufacturer and the vaccine lot number on your cat's medical record, as well as where the injection was given. You may want this information for your records, too.
Watch for firm, painless swellings under your cat's skin near any vaccination site. It's a good idea to run your hands over him regularly so you'll know right away if any lumps develop. Be sure you know the warning signs of feline cancer.
Report any adverse vaccine reactions to both the USDA Center for Veterinary Biologics and to the vaccine manufacturer.
Vaccinations prevent many diseases in cats, but it's important to weight both the risks and the benefits to your cat.
References:
Important Information for Cat Owners
Injection-Site Sarcoma (Vaccine-Site Sarcoma)
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