We need to talk about Feline Injections Site Sarcomas. I will call them FISS from now on. No one really wants to talk about this subject. It makes us uncomfortable. Our whole raison d’etre as veterinarians is to prevent and treat diseases in animals. Now we have to talk about a disease we caused trying to prevent another disease? And it is horrible. Some of the vaccine companies also do not want to talk about it. I am inviting you to get a bit uncomfortable and read on. It’s important.

Thankfully, FISS is also very rare. It depends on your source, but FISS is reported in 1 in 1000 to 1 in 10,000 cats. Most veterinarians will only see a small number of these throughout their career, which is great, but we still need to talk about it.

We need to talk about vaccination protocols.

As a veterinary surgical oncologist, am I the best person to talk about vaccine recommendations in cats? No, I am not. Also, this is no longer a one protocol fits all situation. Here is what I do know, Rabies is a zoonotic disease that is fatal to animals and people. If you live anywhere that rabies is endemic, you have to vaccinate cats for rabies. Even if they stay indoors. Feline leukemia vaccine does not need to be given year after year. Most of these vaccines do not need to be given yearly. I highly recommend that you read the Feline Injection-Site Sarcoma ABCD Guidelines on Prevention and Management (Journal of Feline Medicine and Surgery 2015, 17, 606-613).

We need to talk about vaccine sites.

The recommendations to vaccinate over a limb, rather than an interscapular site, are over 20 years old. The message has gotten through – sort of. The whole idea behind vaccinating over the limb was that when FISS occurred at these sites, it could be treated by a simple amputation. This is less effective when vaccinating over the limb actually means vaccinating over the hip/flank area. This tends to happen when the cat is in a crouched position and also when you don’t actually vaccinate over the limb. If it happens, the resultant tumour in the hip/flank area will require a hemipelvectomy and body wall resection for treatment. This is not exactly what the feline vaccine associated sarcoma taskforce had in mind. You need to vaccinate below the elbow or the stifle. Really? Yes really. Every time? Yes, every time. You can do it! I did it for three years in general practise (1997-2000). You might need to bust out a towel, or a cat bag, or your best cat whispering skills, but it is worth it. While you’re at it, you can explain to the owner why you are vaccinating their cat there and let them know what to watch for in case they develop a mass in this area. What about tail vaccines? Well I am not sure, there is only one study out on this, but to be honest, this is where I vaccinate my own cat. It is a little tricky and I recommend shaving to avoid intra-fur vaccination. Also, there is a sweet spot on the tail that is high enough that you actually have a SQ to inject into, but low enough that you can easily get 5cm margins of tail if an injection site sarcoma forms there. I live in terror that this trend will catch on, but veterinarians won’t vaccinate low enough. I can’t do a cat bum-ectomy. Please don’t ask me to.

We need to talk about what causes this disease.

It is an aberrant response to chronic inflammation. There is a genetic component too, as only some cats seem to be predisposed to this and there are some reports of related cats being affected. This is hard to study because cat families don’t tend to keep in touch.

Vaccines cause inflammation. Vaccines with adjuvant cause more inflammation. That is how they work. There have been case reports of other types of injections causing FISS, including cisplatin, meloxicam and a microchip. These are one-off incidents that are even less likely than the 1 in 1000 to 1 in 10,000 cats that are getting FISS from vaccines. Some vaccine companies like to focus on the fact that other injections have been reported to cause this disease. Yes, this is true, but adjuvanted vaccines is a thing we can change and giving other injections may not be. Instead of throwing up our hands and saying, “Well any injection can cause this” let’s focus on the thing we inject into cats more than anything else – vaccines. We need to stay focused on the vaccines because they are the biggest part of this equation. We can actually decide when to vaccinate and where. This is where we can move the needle. The other side to this is that we can’t get complacent with the nonadjuvanted vaccines and start vaccinating all willy-nilly anywhere we want to because nonadjuvanted vaccines are “safe.” Stick to the distal limbs with all vaccines.

We need to talk about vaccine records.

Vaccine records are not sexy, but they are so important. The type of vaccine, lot number, expiry date and vaccine site need to be recorded. If the cat develops FISS, this needs to be reported to the vaccine company because it is an adverse event. This is a highly aggressive fibrosarcoma. It really doesn’t get any more adverse than that. As an added bonus, when you have all of this information, a lot of vaccine companies can be really great about helping the owner to treat this disease. I mean dollars in their pockets to help with the cost of diagnostics and sometimes even therapy. I have had vaccine companies give between $1,000 to $4,000 to my clients to help with treatment. Please report these to the vaccine companies. And, hey, giving these companies all of the information about a FISS that occurred with their vaccine might help them to understand what is going on better. Science!

We need to talk about what to do when you see a mass at an injection site.

Hopefully you have an educated client who will come back if a mass develops at a vaccine site. Hopefully the mass is small and located below the elbow or the stifle. Hopefully you will recognize this may be an injection site sarcoma. Most of the time, a fine needle aspirate is a great test to do on a new mass. However, in the case of FISS, cytology is not your friend. It might lead you to believe that this is just inflammation. You can do an FNA to rule out other tumour types if you want, but ultimately, you are going to need histopathology. An incisional biopsy should be performed on masses that have been present for more than a month after vaccination. The goal is to get a small amount of tissue and to leave the mass intact so that it can be removed with wide or radical margins if it is a FISS. Excisional biopsies are problematic because they can make definitive resection much more difficult and, let’s face it, this is already difficult.

We need to talk about how we are removing these.

Current recommendations are 5cm radial margins and two fascial planes deep. If you think about the smallest FISS we diagnose, it is around 2cm. If you take 5cm margins, that is a 12cm diameter defect – in a cat. It is usually successful if you are lucky enough to get an early diagnosis and a location that is amenable to a radical surgery. These are two things that we have control over by educating the client, doing an excellent work up and placing the vaccine in a location where we can get 5cm margins.

I used to enjoy of the challenge of a big FISS surgery. Now I just feel sad when I treat these cases and I need to do a hemipelvectomy and/or body wall resection. This is because I know that if the vaccine had been placed low on the limb, I could have achieved the same or actually much better with a simple limb amputation. These cats are breaking my heart. I honestly can’t do any more lectures on huge cat-ectomies for this terrible disease. I can’t do another panel discussion at a conference arguing the finer points of whether we should do radiation before we remove a huge portion of cat or after we remove a huge portion of cat. It is ridiculous. The answer is we shouldn’t be doing either of these things. We need to do better as a profession and do whatever we can to decrease the incidence of disease, diagnose it earlier, and make it easier to treat. Please let’s work together on this. I know it is only 1 in 1,000 to 1 in 10,000 cats, but to cat owners going through this, this cat is one in a million.

Thanks for the talk.

Things We Can Change
Don’t over vaccinate. Create protocols that are appropriate for the level of risk
Consider using non-adjuvanted vaccines
Vaccinate below the stifle and elbow
Focus on gentle handling of cats to allow you to vaccinate low on limbs
Record every vaccination and site in your medical records
Educate clients on what to look for and what to do if a mass develops
If you see a mass at an injection site, do an incisional biopsy without delay
Report FISS as an adverse event
Wide or radical excision as the first, curative surgery

Things We Can’t Change
Some cats are predisposed to developing FISS at sites of chronic inflammation
FISS is an extremely aggressive tumor that requires aggressive resection
Cats need to be vaccinated for rabies
Some cats do not care for the veterinary clinic/vaccine experience


The views and opinions expressed in this article are those of the author and do not necessarily reflect the position of the DrAndyRoark.com editorial team.


Sarah Boston is a veterinary surgical oncologist and public speaker. Sarah is also a cancer survivor and author of the best-selling, hilarious memoir, Lucky Dog: How Being a Veterinarian Saved my Life.

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