You may have hear or read on the internet that vaccines cause cancer in cats. It is enough to scare any caring cat owner into rethinking about the safety of these lifesaving vaccines. It is true that a rare cat will get a true “allergic” reaction to a vaccine, just like dogs or humans. Vaccines have foreign proteins that we inject into their bodies. But it is also true that injections (any injection) CAN cause a reaction that can lead to a sarcoma in a rare cat. Lots of epidemiological studies have to done in the last 25 years to find out WHAT is causing the inflammation, WHICH vaccines, WHAT manufacturer, and WHY cats might develop this terrible disease
The current thinking is that individual cats may respond to inflammatory changes in a manner that predisposes to sarcoma formation. Current studies to investigate the cytogenetics of injection site sarcomas may provide more information. Up-to-date information regarding research can be obtained from the Vaccine Associated Fibrosarcoma Task Force.
What is the incidence of injection site sarcomas? Most studies agree it is 10-100cats with sarcomas/100,000 cats vaccinated, so about 0.1-1% of vaccines. There does seem to be some regional variation, but they are reported worldwide.
What injections area associated with sarcomas? All vaccines, long acting steroids, subcutaneous fluids, and antibiotic injections
At first vets thought it was only vaccines, and we saw a higher incidence with killed vaccines (Rabies and Feline Leukemia Virus also called FELV) , and especially if aluminum was used as adjuvant. So Garden Ridge Animal Hospital switched to recombinant non -adjuvented FELV and Rabies by Merial like many other vets. Later we saw that all vaccines types made by all the manufacturers have some association. If a cat received all the vaccines in same location, like the neck, there was a higher incidence of sarcomas, so we split them up now. The recommended sites are NOT the neck anymore, but Rabies on Right rear leg, Leukemia on Left rear leg, and FVRCP on the Right foreleg.
Why do cats make sarcomas at injection sites? One theory speculated about a viral helper to FELV, the Feline Sarcoma Virus, but only a few cats with sarcomas test positive for FELV or FIV. Another theory is gene mutation, oncogenes, and mutations in tumor suppressor genes. Approximately 75% of injection sarcomas were found to contain p53 and c-kit oncogene. Approximately one third of tumors contained both p53 and mdm-2, and these tumors were histologically more anaplastic, perhaps explaining the aggressive biologic behavior of some injection site sarcomas.
Any injection can cause local inflammation, usually in first few weeks after the injection. If a bump is present less than 1 month, it should get checked out with a needle biopsy. If the biopsy is “suspicious”, then aggressive surgery is indicated and maybe presurgical radiation therapy. These Injection Site Sarcomas are scary because they are aggressive, large (greater than 4 cm), invasive, and can metastasize to other parts of the body.
There is a lot we still don’t know about Feline Injection Site Sarcomas. I have seen 3 or 4 in my 28 years at Garden Ridge Animal Hospital. One was a cat that I had vaccinated, but not exclusively. But over my 35 years as a vet, I have seen many more cases of Feline Leukemia, Distemper, respiratory infections and even feline Rabies. We also vaccinate less frequently than years ago, and we talk about a risk assessment at our yearly exams. For examine, I don’t recommend FELV vaccine to indoor only adult cats. FVRCP is every three years once they are adults, but Rabies (required by state law and a real threat in Denton county) is still annually with the non-adjuvented Merial Purvax.
I know vaccines save kitty lives and improve quality of life a hundred fold over the risk of Injection Site Sarcomas. If you are still worried, please come in with your cat and we can at least perform a yearly health checkup. Vaccines are always optional, and not the only reason to see a vet. Our staff is standing by.
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