Can my cat get cancer from vaccinations?

Aha, yes. The unfortunate answer is yes, they can. There is an injection site tumor called a fibrosarcoma that they can sometimes develop. I have been in practice for 21 years and I think I have seen three in 21 years. Is it common? Obviously, no, it’s not common at all. In fact, there've been a lot of changes to vaccines in probably the last 10 to 12 years or so, and I'm just randomly picking that timeframe, but around there, to where they changed it. It used to be due to what's called the adjuvant, the carrier in the vaccine. They would put an additive in vaccinations to stimulate the immune system and it's thought that a lot of the adjuvants in some of the vaccinations, particularly the old leukemia vaccines, were thought to be the ones to do that. To my knowledge, that adjuvant has been changed or taken out completely. I don't know for certain, but I can tell you that I have not seen a reaction that way in many, many years—it’s probably been double-digit years since I've seen one of those cases, but it is possible, unfortunately.

Yes, and this is true even more so with cats than dogs. They have this weird reaction where they can get something called an injection site sarcoma. And oftentimes it has to be addressed, maybe even surgically.

Technically, yes, but that is even rarer. This has been known for years. The numbers haven't changed a whole lot in how common it is, although you'll see some, one in 1,000, 1 in 10,000. It does appear to have a genetic nature to it, but it is a rare occurrence. However, if it were your cat or my cat, I mean, who cares if it's rare. It's significant, and it's a big deal. It's a big problem, but it's not a reason to be afraid of vaccines. The benefits of vaccines far outweigh that risk. Still, if you have a cat that you know is related to a cat that had one of those cancers related to injection, then we would have a serious talk about whether or not your cat should be vaccinated as well if they're actual siblings. So the risk is there. It is pretty low.

I guess another thing to think about, too, would be the recombinant vaccines. I know we haven't talked about that a whole lot, but that's part of the reason why those came out. There are different ingredients in vaccines. An adjuvant is a common word that they use for extra ingredients, and some of them are designed to cause stimulation to further make the immune system react to the vaccine. Well, they aren't sure, and they do see some link potentially to that. But the more reactive a vaccine could be for a cat with a genetic predisposition, that might make that cat more likely to get a cancer response to certain vaccines.

That's the reason we talk about the recombinant rabies vaccine, the non-adjuvanted rabies vaccine, and leukemia vaccines that come in that form where we talk about the risk versus benefit of considering one of those vaccines as it may decrease the risk for cancer in some cats.

Yes, in very rare situations, there are injection site sarcomas that have been linked to vaccinations. They're rare, occurring in about one out of 100,000 vaccinations, but they are called injection site sarcomas.