Prevent Vaccine-associated Sarcoma

Some vaccinations can cause a cancer to form where the vaccine was given to a cat

Published: September 04, 2018
Photo courtesy of Morguefile

Have you ever questioned vaccination for your cat? “Anti-vaxxer” sentiments are common in the media, and naturally, we all want what’s best for our pets (and ourselves and our family). But just because some people are obnoxiously loud about something doesn’t make it true.

Vaccinations are a miracle of modern medicine. The first vaccine for smallpox was created from cowpox, which is similar to smallpox. Dr. Edward Jenner in the 18th century inoculated a child with cowpox from the milkmaid to “teach” the kid’s immune system to recognize smallpox and fight it off before causing infection and disease. Then he gave the kid an injection of smallpox. Lack of scientific ethics and informed consent notwithstanding, the boy did not develop smallpox. Born was the concept of vaccination, named for the Latin vacca, or cow.

The incidence of many human and animal diseases have been greatly reduced, and even eliminated, in the modern world thanks to vaccination.

Your cat probably receives some combination of the following vaccines:

  • Nearly all cats have herpes. It is not the same herpes that people have. You won’t catch herpes from your cat. As in people, herpes in cats is forever. Cat herpes causes the kitty “common cold.” The vaccine for herpes doesn’t prevent a cat from catching herpes, but it reduces illness when their herpes acts up during times of stress.

  • Calcivirus and panleukopenia. Calicivirus is another common respiratory virus in cats. Panleukopenia (or feline distemper) is similar to parvovirus in dogs, causing debilitating infection that is life-threatening to kittens.

  • Depending on where you live, rabies vaccination is legally required for all cats, dogs, and ferrets. Rabies is practically 100 percent fatal to people, so actually we vaccinate pets not only to protect them from rabies, but to protect the humans around them as well. In countries where rabies vaccination and animal control is less successful, tens of thousands of people die from rabies every year.

  • Leukemia virus. Yes, there is a virus that causes cancer in cats. This vaccination, along with the indoor lifestyle of most cats, has helped reduce the incidence of this fatal disease. Not all cats need this vaccine past kittenhood.

I absolutely believe that vaccination is necessary for cats to lead a healthy life. Life-threatening side events are rare.

However, I want to focus on one of those rare, but potentially preventable, effects: vaccine-associated sarcoma (VAS). You read that right. Some vaccinations can cause a cancer to form where the vaccine was given to a cat.

That is super scary and probably makes you want to join the ranks of the anti-vaxxers. But trust me: you don’t have to do that. Let’s use science to figure this out!

VAS is rare. Probably less than one in 10,000 vaccinations will result in a sarcoma. But if your cat becomes that statistic, it’s certainly heartbreaking.

These tumors grow deeply into skin, muscle, and even bone. A routine tumor removal surgery will not cure them. Wide margins of at least two inches on all sides of the tumor need to be removed, plus a couple layers of tissue deep to the tumor. Radiation treatment may help. A CAT scan (no pun intended) can help a veterinary surgeon or oncologist determine how invasive the tumor is.

One strategy to save cats from developing VAS is for the veterinary staff to inject vaccinations toward the end of the leg. We do this because if a VAS develops far enough down a limb, we can solve this problem with simple logic by amputating the leg. The way we think of it, a cat actually has three legs plus a spare.

Some cats may be genetically predisposed to developing these tumors. We can’t control or predict that.

Another theory, which I am convinced is the biggest factor in development of VAS, is that adjuvants contribute to tumor formation in cats. Adjuvants are substances commonly added to vaccines to boost the body’s immune system so it will react more effectively to the bug in the vaccine. This is not an inherently bad thing — except for cats.

Your cat needs vaccinations according to her lifestyle and your local laws in order to prevent common or severe diseases. However, ask if your clinic carries non-adjuvanted vaccines for your cat. The two vaccines usually responsible for VAS are adjuvanted leukemia and rabies vaccinations, so speak to your veterinarian about your cat’s lifestyle and what vaccines are truly needed and how often. Most cats do not need every vaccine every year. Monitor any vaccination site closely for development of a lump and alert your vet if you notice anything. Unfortunately, these tumors can form years after vaccination.

Vaccines are safe, effective, and necessary for the health of people, pets, and livestock. But it is possible to have too much of a good thing, so be proactive in the health of your cat and vaccinate smartly. 


Christy Corp-Minamiji, DVM
May 18, 2021

Hi Paula, it's good that you're so concerned about your cat; you clearly love her very much.  But in this case, I don't think you need to worry.  In getting her rabies vaccine, you've protected both her and your family from a highly fatal disease (rabies).  As the article mentions, vaccine associated sarcomas are pretty rare and many veterinarians have switched to non-adjuvanted vaccines.  Everything we do in life (including getting out of bed) comes with risk, and we always have to weigh the risks against the benefits.  In this case, I think the benefits of the vaccine outweigh the risks.

May 15, 2021

I am so worried now. I didnt want the 3yr rabies vaccine for my cat, but I let them give it to her. I will be callibg tomorrow to find out if it had advantunt in it. I sure hope not.

Millie Portante
September 18, 2018

My cat, Kayla I believe was the one in 10,000. She had a tumor removed in June 2009 and by September there was nothing more that could be done for her. I would get her all the vaccines to make sure that she wouldn't get sick. In the end it was all the vaccines that I got her is what made her sick. I am still heartbroken over this loss.

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