All you cat owners out there are likely to know about the infamous, vaccine-associated sarcoma. You may not know it by name, but you’ve doubtless heard about the aggressive tumors cats can get at their vaccine injection sites.


But here’s something you might not have heard yet: This month, the Journal of the American Veterinary Medical Association reported something exciting: The incidence of these tumors is down from 1 in 5,000 to 0 in one million — in this one published study.


Here’s the back-story:


Uncommon though they are, these tumors are notoriously aggressive and have been associated specifically with vaccine-type injections, though (theoretically) almost any injection could have caused it.


Most cancers don’t need a good reason — they just happen. But when tumors crop up right where injections have been administered in the past, it’s irresponsible for us to turn a blind eye to this possibility. (By “us,” I refer to those of us in the business of veterinary practice, science, and industry.)


What we suspect is that vaccines create inflammation in the skin. In an attempt to address this insult, a cat’s immune system can get confused and enables cancer cells within normal skin.


Fortunately, these cancers aren’t of the wildly-spreading variety. They are, nonetheless, extremely hostile to the tissues they invade. As a result, aggressive surgery of these tumors is the mainstay of treatment. According to veterinary surgeons, that means removing wide swathes of skin and muscle (and sometimes bone) surrounding the tumors.


According to the American Veterinary Medical Association’s Vaccine-Associated Feline Sarcoma Task Force, the situation is best managed by injection of vaccines in spots far away from the shoulders (historically, the most common site for tumors and among the most difficult sites to address surgically). They also recommend using as few vaccines as necessary during a cat’s lifespan, but caution that you should never forego infectious disease prevention because of this infrequent outcome.


The more cynical among you might think this sounds like “committee-speak,” the kind of talk meant to protect vaccine-pushing vets and the companies supplying them, while still hedging their bets on the safety issue.


Truth is (my cynicism currently at bay), I’m in their camp on this one. While I certainly don’t consider myself a vax-pusher, I’m by no means on the no-vax, alternative medicine-exclusive bandwagon, either. I may be self-aggrandizingly misguided here, but I like to consider mine a balanced perspective based on science, not commerce, and not alarmism.


This crisis in feline vaccine-associated sarcomas has been evolving for twenty or more years. Once an “association” was established between vaccines and these tumors, the industry got moving. Though, in retrospect, an outsider might observe a mighty-slow move towards action (especially considering the severity of these tumors), even I (ever the cynic) was surprised by the alacrity of the response within the veterinary industry.


The feline practitioners came out en-masse. The Universitarians had their say (and then some). The AVMA coordinated its Task Force. Vaccine manufacturers changed their recipes (albeit quietly to discourage litigation, no doubt, but also in deference to its acknowledged responsibility). And the rest of us vets, slowest to act, were left to our own devices.


Ever so cautiously, we’ve changed our tactics: vaccinating less and vaccinating under the skin of the lower hind limbs, as goes the recommendation of the Task Force. (Callous as it sounds, it’s much easier to remove a hind limb than a spine should a nasty tumor ensue.) But, as a profession, we’ve been sloooow to enact these measures.


Many of us vets still flout these recommendations, citing poor evidence of causality in tumor creation (sure, that’s why we call them vaccine-“associated” tumors), prevalence of infectious disease (which many still contend requires yearly vaccination), and the need to maintain an annual vaccine schedule so clients will present their cats for exams (that’s got some merit but that doesn’t hold water with most of you, does it?).


And, truth is, statistically speaking, our cats are better off vaccinated and at risk of sarcomas than unvaccinated and 100% sarcoma-free. Infectious diseases kill more commonly and more effectively than these cancers do. But there’s a balance somewhere, isn’t there? I think so. It’s called “minimized vaccination schedules”; give what’s needed and give no more.


Because of all our efforts, slow adopters in the vet profession notwithstanding, the rate of these sarcomas seems to have fallen off almost completely. In this case, I give kudos to the feline-exclusive practitioners, the AVMA, relentless academicians and vaccine manufacturers (backside-sensitivity is a good thing and responsible action, even better). The rest of us vets? We’re just hangin’ on the coattails of our betters on this one.


Sometimes our best efforts fail us in veterinary medicine. No vet wants to see a patient afflicted with a serious disease he or she inadvertently caused while undertaking to prevent another. But we’re charged with the responsibility to do our best — and sometimes that means adopting the recommendations of the more cautious among us. In this case, I think they’ve proven themselves worth listening to.


Learn more:

2013 AAFP Feline Vaccination Advisory Panel Report


Canine and Feline Vaccination Guidelines


Feline postvaccinal sarcoma: 20 years later


Origins of Injection-Site Sarcomas in Cats: The Possible Role of Chronic Inflammation—A Review



Image: Natata / Shutterstock


This page was last updated on 5/27/2015