Hi stranger! Signing up for MypetMD is easy, free and puts the most relevant content at your fingertips.

Get Instant Access To

  • 24/7 alerts for pet-related recalls

  • Your own library of articles, blogs, and favorite pet names

  • Tools designed to keep your pets happy and healthy



or Connect with Facebook

By joining petMD, you agree to the Privacy Policy.

petMD Blogs

Written by leading veterinarians to provide you with the information you need to care for your pets.

The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

Vaccine-Associated Sarcoma and Your Cat

A few weeks ago, I wrote about the importance of all cats being vaccinated against rabies. I touched briefly upon a possible side effect of vaccination — cancer developing at the injection site — but the topic warrants a bit more attention, so here we go.

 

The official name for this type of cancer is vaccine-associated sarcoma (VAS). There are a lot of different types of sarcomas out there. The one that is most commonly seen at injection sites is called a fibrosarcoma, but other sarcomas are also possible (e.g., malignant fibrous histiocytomas, osteosarcomas, rhabdomyosarcomas, liposarcomas, chondrosarcomas, and undifferentiated sarcomas). The different names relate to exactly what type of cell has become cancerous.

 

All of these sarcomas can and do develop in cats that have not been vaccinated, particularly if a cat is infected with the feline sarcoma virus, but they are pretty rare. So, if one develops at the site of a previous injection, it is generally assumed to be caused by that injection.

 

Sounds simple, yes? Well, unfortunately that is not always the case. VAS can develop anywhere from a few months to many years after an injection has been given, and veterinarians have not always been good about writing where injections are given in a pet’s record. This is changing, as injection sites for vaccines are becoming standardized (rabies right rear leg, feline leukemia left rear leg, feline distemper right front leg), but before VAS was recognized as a serious problem, many vets simply gave any injection wherever was easiest (often between the shoulder blades) and didn’t bother to record the location.

 

To complicate matters even more, older rabies and feline leukemia vaccines (those that contain killed, whole viruses and adjuvants to increase the immune response) appear to be the culprits in many VAS cases, but the disease has also been associated with other injections that can cause a significant amount of inflammation at the injection site (e.g., long-acting steroid injections). The thought is that inflammation is what causes cells in the area to mutate and become cancerous, and some cats may be genetically predisposed for this to occur. The website for the American Veterinary Medical Association’s Vaccine-Associated Sarcoma Task Force is an excellent place to go if you are interested in the nitty gritties of VAS.

 

To reduce the likelihood that your cat will develop a vaccine-associated sarcoma, make sure your veterinarian is following the American Association of Feline Practitioner’s vaccination guidelines, and that non-adjuvanted vaccines are used whenever possible. Also, give your cat oral medications versus long-acting injections (e.g., prednisolone pills versus a repositol steroid), if you are able to do so.

 

VAS can be successfully treated, but it may take radical surgery, sometimes in conjunction with radiation treatments and chemotherapy, to do so. Amputating an affected leg has the greatest chance for affecting a "cure," which is why vaccines are now given low down on the legs.

 

Watch your cats for new lumps and bumps, particularly around injections sites. Do not panic if a small bump appears soon after a shot is given. As long as it goes away within a month or so, it is nothing to worry about. But any mass that persists or grows over time should be checked out by a veterinarian.

 

Dr. Jennifer Coates

 

 

Image:  / Shutterstock

Comments  2

Leave Comment
  • 03/30/2013 12:47am

    Wow.

    You are a person after my own heart.
    Here it is a few years later,
    and after scouring the vet journals available to me, a layperson, and both the Task Force and AAFP literature,
    I couldn't find much more info either,
    other than the study Dr. Meade here mentions in her reply to you.
    I did find some intial studies suggesting a p53 gene mutation link which would mean the cats ability to contain the inflammation from becoming cancerous is hereditary. I think.

    But that still doesn't absolve vaccinations (and/or injections, and/or adjuvants overall) as the trigger.

    It just means you'd have to know your cat's heritage. I don't know about you, but I acquire my feline friends from farmers, and as strays or ferals who decide to give me a chance at loving them.
    I don't have purebreds, so...
    a vet saying (as one has just this week): "Well, we've only seen a handful of cases of VAS in 20 years, so the families of cats around here aren't much at risk"
    doesn't really persuade me to dismiss VAS as a possibility.

    I shall try to stick with initial CORE vaccines, and then following only my state's Rabies law requirement re-vaccinating.
    Dr. Schultz' and Scott and Geissinger's work on this I hope will turn the tide for good on the yearly vaccination protocol myth.

  • Spindle cell sarcoma
    09/24/2014 12:49pm

    My tortishell, Molley, developed a white patch at the site of her injection. She was brown, Black and Tan. I asked the vet repeatedly why her hair changed color and was told it was nothing until a lump began to grow and it hurt her when I touched it. A biopsy showed the above cancer. I was told that it was grave and aggressive. It came back quick. After a few trips to the vet to have it aspirated and hearing Molley react, I gave her back to God. The people who gave her the shot said that it could sometimes happen with the three year rabies shot but not the one year. I am presently not vaccinating my other cat who is an indoor cat and my vet agrees with it.

Meet The Vets