Vaccine-Associated Sarcomas in Cats

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What is a vaccine-associated sarcoma (VAS)?

A sarcoma is a type of cancer that affects mesenchymal cells, which can be found in tissues such as fat and muscle.  VAS is a sarcoma that is potentially induced by a vaccination. The real cause is a genetic predisposition which can cause the effected cat’s inflammatory cells to get out of control and release a substance that causes DNA damage.  It is normal for a vaccine to cause a little localized inflammation. It is only in a small minority of cats (about 1 in 10,000) that this inflammation can get out of control ultimately leading to a sarcoma. This situation is very rare, but concerning if it does occur.

My cat has a bump at his vaccination site, should I be worried?

Often, cats will have a slight inflammatory reaction and a small granuloma (bump) will form. A granuloma is not a concern and should go away in a few months. However, if the bump does not go away or continues grow, you should talk to your veterinarian about testing the lump to determine if it is cancerous. 

What if my cat’s lump ends up being a sarcoma? Will my cat be okay?

At this point, you and your veterinarian will discuss treatment options. This may includes surgical removal of the lump, radiation therapy, and chemotherapy. The extent of treatment necessary is very dependent upon your individual animal and how far your animal’s cancer has progressed. Though rare, this is a cancer, and a very serious disease and prognosis will depend heavily on the extent of disease present and response to treatment.

Even though it’s rare, why even take the risk? Should I continue to vaccinate?

Yes! This may sound like a simple answer but neglecting core vaccinations will likely do your pet more harm than good. Vaccinations are given for a reason and they are often to prevent very nasty and often fatal diseases. Some of these diseases, such as rabies, are also zoonotic (can infect humans). If you avoid vaccinating your cat you may end up not only putting your cat at greater risk for infection, but putting yourself and others in harms way as well.

Can I at least limit the amount of vaccinations I give?

Yes – you and your veterinarian may discuss if there are certain vaccinations that may not be necessary. These vaccines will most likely be vaccines for certain diseases that are not prevalent in your area or your cat will unlikely be exposed to. To reduce the risk of sarcoma further, our hospital uses the PureVax line of vaccines specifically formulated for cats without an adjuvant so post-injection inflammation is even less likely.

Have questions about your cat’s vaccines? Please ask! We are happy to address any specific concerns you may have about your furry family member. That’s what we are here for!