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Feline Injection Site Sarcoma: Yoda’s Cancer Story

If you follow Yoda’s travels on our Instagram page, you might have seen our fluffy kitty receiving some extra love, care and cuddles after numerous vet visits, one big operation and several radiation treatments. 

That’s because Yoda, we discovered, has developed an aggressive form of cancer called Feline Injection Site Sarcoma (FISS). 

As tough as this process has been for us and our furry warrior, the online cat-lovers community has been so helpful and caring. We couldn’t be more grateful for both the emotional and financial support we have received. 

So as a token of our thanks, we wanted to share Yoda’s cancer story with you, as a way to help inform other pet parents about this issue.

By doing this we hope to increase the visibility of this condition, by bringing awareness to the symptoms, causes, and what you could do to help minimize your cat’s chances of developing FISS.

We’ll cover:

  • What is injection site sarcoma in cats
  • What causes injection site sarcoma in cats
  • Yoda’s journey through treatment and amputation

⚠️ Brittany, Paul, and the Fluffy Kitty team are not veterinarians. This article is based on facts, research, and personal experiences. We provide you with the best information we can but you are of course free to follow our advice or not. Paul and Brittany (and Yoda) shall in no event be held liable for any loss or other damages including but not limited to special, incidental, consequential, or any other damages.

Discovering Yoda’s Mass

We first discovered Yoda’s suspicious lump while living lakeside in Guatemala. We were enjoying a travel stop in a tiny home that was perched on the gentle slopes of an ancient volcano, peering out over Lago de Atitlán. 

It was here where Yoda enjoyed daily outdoor adventures inside our enclosed grassy property. After a fun and innocent day of climbing trees and getting chased (by us), we smoothed a hand down Yoda’s back and discovered an unusual lump

The main symptom of an injection-site sarcoma is a tumor, or mass, around the location of the injection. Most tumors form within a few weeks, but they can form up to 10 years after the injection. The tumors are usually firm, and around 1-3cm to begin with. 

The Initial Visit to the Vet

Surprised at the sudden size of the lump, we scheduled our first visit to the local vets in Guatemala. Yoda must’ve felt anxious that day, or perhaps could feel the anxiety coming from us, and he reacted badly to being examined. 

At this point, we were advised to put Yoda under sedation in order for the vet to be able to shave his mass and do a fine needle aspiration.

Fine needle aspiration is a type of biopsy where a needle is inserted into a lump or mass to help determine the cause. 

This was Yoda’s first time being sedated, and I was uneasy about it. It didn’t help that we weren’t at all advised or warned of the risks involved.

Sadly, Yoda was given too much medication and almost was unresponsive.

As you can imagine, this terrified us. Not only by the possibilities of what the lump could be but also by seeing how this was just the beginning of the invasive poking, prodding, and procedures that Yoda might have to endure. 

The vet concluded the mass was suspicious. However, until a fuller biopsy was made there was no telling if it was cancerous or not. After such an unsettling experience, we decided there was no way we would be returning to have the same vet perform a biopsy on the mass…

Second Vet Visit

We kept our eye on the mass over the next 4 weeks, while we transitioned from our temporary home in Guatemala back to the USA, where we would spend the summer with family. Over this period, the lump didn’t grow much, and it didn’t seem to bother him.

It wasn’t until the first week of July, nearly 8 weeks later, that we noticed a definitive growth in the mass. 

We scheduled another visit to the vet, this time in the States. Within minutes of the vet checking Yoda’s mass, we were told he definitely had cancer and wouldn’t have long to live. That day was awful… It felt like we’d already lost him and the tears wouldn’t stop rolling.

The vet was 99% certain that Yoda’s lump was an injection-site sarcoma.

What Is Feline Injection Site Sarcoma?

Feline injection-site sarcomas (FISS) is the name for cancerous tumors that develop on the injection site of a cat’s body. The tumors often develop in certain areas – between the shoulder blades, in the hip region, and in the back legs.

What Causes Injection Site Sarcoma in Cats?

The true cause is not yet fully understood. However, there is a definite association with the administration of long-acting injections, like vaccinations.

The most agreed-upon cause is a prolonged inflammatory response to the injection itself (not the vaccine administered), which can lead to FISS developing. 

Yoda’s Tests & Pre-Treatment

While our vet was almost certain that Yoda’s lump was FISS, they still needed to run tests to see if the cancer was isolated or had already ‘metastasized’, or spread, to the lungs.  

Yoda’s feline injection-site sarcoma diagnosis went as follows:

  • Needle aspirate – results were sent to a lab, which came back with a high likelihood that the mass was indeed FISS. To confirm this, the vet also performed:
    • CT scans
    • Bloodwork
    • Chest x-rays

Note — the FISS diagnosis was officially concluded after his amputation, not before, once they were able to remove the leg and send it for examination by the Pathology Department. Chest x-rays and bloodwork were necessary to see if cancer had metastasized (spread) to the lungs or to rule out any other underlying disease.

Feline Injection Site Sarcoma Treatment

Research suggests that the most effective method of FISS treatment includes combining localized surgery, to remove the cancerous area with room for ‘clean margin’, along with radiation therapy. 

Yoda’s Treatment Begins

Amputation is typically the solution for FISS, but we were told this was not the case for Yoda (at first). As his mass was so high up on his leg, near the hip joint, we were told that surgery, coupled with radiation, was the most likely course of action. 

However, our vet made it clear that it really depended on what the oncologists had to say.

Veterinary oncologists are specialists in animal cancers. They decide the most appropriate course of treatment and coordinate the treatment program with your everyday vet. 

To follow up with surgery and radiation would mean transferring to another practice in a different city, a couple of hours away.

Three weeks went by as we waited for our first appointment and initial assessment at the University of Tennessee Veterinary Medical Center.

Feline Injection Site Sarcoma Surgery: High-Limb Amputation

I went to our assessment on August 10th with Yoda and really didn’t know what to expect. 

Once again, they took Yoda for blood work and CT scans, to see if new masses had appeared since his other scans – which were already a couple of weeks outdated. His reports came back clear, other than persistent anemia (likely due to the tumor).

I waited for almost 10 hours that day. When I went to pick Yoda up it was confirmed to us in plain terms: Yoda most likely had Feline Injection Site Sarcoma.

Our two options were:
  • Option A — high-limb amputation, most likely followed by radiation therapy.
  • Option B — a hemi-pelvectomy, involving removing parts of his pelvis, and likely followed up by radiation therapy.

After assessing the CT results, amputation was now recommended. We were assured it was the best way forward for saving both Yoda’s life and preserving the quality of it too.

Amputation was scheduled the very next morning on August 11th

It came so suddenly, and I was not at all prepared, especially since Paul was unable to accompany me due to travel restrictions into the US from the EU. This meant it was just Yoda and me alone, and I quickly booked a hotel for us at the last minute. I rushed off to the store to buy Yoda some fresh tuna filets and a comfy bed, and a toothbrush and toothpaste for myself.

Somehow I managed to keep it together.

That last night with Yoda went by too quickly. We cuddled and I tried to reassure him as much as I could. But sadly, before I knew it, I was putting him in his carrier again.

Yoda’s Surgery & Getting Him Home

The next day, I dropped Yoda off early (around 7 am) and drove home. I received a call around noon that all went well! The surgery was a success and Yoda would be in recovery for the evening.

Yoda wasn’t expected to come home the next day, but he did so well overnight that they released him early. I drove back and picked up my shaven, three-legged boy the next day. 

Our ‘Mr Nug’ was now officially ‘Mr Nub’!

Post Amputation Home Care

The amputation was really only the beginning – something I realized quickly. 

For the first 14 days, Yoda needed medication almost every 8 hours. I was sent home with detailed care instructions. This included that he must wear his e-collar/cone 24 hours a day to prevent him from licking/removing his sutures (the only exception being during meals and whenever I was able to watch him very carefully). 

After 14 days, Yoda had his initial visit at the Radiation Oncology department, at yet another veterinary practice in another city — from Tennessee to South Carolina we went! That same day he finally got his stitches removed. Thankfully the incision site looked clean and was healing well. 

Radiation was necessary, they told us. We had hoped this wouldn’t be the case, seeing as how the ‘margins’ the surgeons got seemed to have been so successful. 

But as our radiation oncologist explained, this just wasn’t enough. Without further treatment, cancer would likely come back within weeks or months.

Per our radiation oncologist, feline injection-site sarcomas are still underresearched and quite a mystery. They only know that the mass begins after injection, most often from a vaccine, but even as small as a prick for diabetes can start it. He suggested that the inflammation which results from an injection is actually aggravated (purposefully) by traces of aluminum alloy so that the body reacts to the vaccine and can build up antibodies. However, for some cats, this prolonged inflammation can oftentimes stay ‘angry’ and become malignant.

Radiation Therapy Sessions

Cats, we were told, apparently do very well with radiation and experience minimal side effects. So, despite the sudden financial burden, we decided to move forward with radiation therapy treatment. This involves 20 total sessions – one a day, Monday-Friday, for four consecutive weeks.

Side effects of radiation treatment in cats are likely to appear in the final days of radiation, and may include:

  • Dry, flaky skin (similar to a harsh burn)
  • Moist desquamation (thin skin that weeps and scabs)
  • Diarrhea, loose stool

We’re pleased to say that as of September 27th, Yoda is now 75% done with radiation. 

So far, he has had minimal effects and is his happy, curious self. We even got to go outside recently and walk him on his harness and leash for the first time since amputation.

Since we chose not to board Yoda during the week, he comes home every day after his session.

Yoda must wear his catheter on weekdays, which we flush each night. He gets dropped off around 9 am, and we pick him up only 3 hours later around noon. This means he doesn’t spend very long at the hospital and gets to cuddle up with us at home the rest of the day and night. 🙂

Although radiation doesn’t guarantee that cancer won’t come back, we are staying hopeful that Yoda makes up the 50% of cases in which cancer doesn’t grow back or spread in 2+ years. 

Still, it’s about managing cancer now and preserving Yoda’s life as long as possible. But FISS is aggressive, and it’s likely that it will ultimately reduce how long Yoda gets to live. We just don’t know how long.

All we can do is be grateful for his surgery and radiation being successful so far, and enjoy every moment we can with him by staying in the present wherever possible. While it’s tricky not to mentally zoom ahead and worry, Yoda is a constant reminder that cuddling up and enjoying each other’s company is what matters right now. 

How Common Is Feline Injection Site Sarcoma?

Since sharing Yoda’s story, we have come to discover just how many cats and pet parents have to go through this traumatic experience. 

Research suggests that 1-10 of every 10,000 vaccinated cats will develop FISS.

We were sure we weren’t the only ones entirely unaware of the possible consequences of these vaccinations. This leads us to ask – is this suffering necessary? 

Can You Prevent Feline Injection Sarcoma?

If we’d known what we do now, we often ask ourselves… Would we have kept getting Yoda’s vaccinations updated through injection every year when there are, as I was told, some oral alternatives? 

Or perhaps why vaccinate at all, if your cat stays indoors all its life? 

Why Vaccinate?

Vaccines help our cat’s immune system fight infections from disease-causing microorganisms. They prepare a cat’s immune system to fight serious infections much more quickly and efficiently, which is why they are widely used. 

While skipping vaccinations for fear of your kitty developing FISS might bring peace of mind, this could be putting them at risk anyway, especially if your cat roams outdoors. Plus, individual states also have strict rules about rabies vaccine requirements for cats. 

No vaccinations can also mean your travel will be extremely limited too. We even had to show proof of rabies vaccination to the vet when going for Yoda’s radiation therapy treatment — they require it, understandably.

What About Alternative Vaccinations?

Some researchers now argue that “non-adjuvanted, modified-live or recombinant vaccines should be selected in preference to adjuvanted vaccines.” These are alternatives to the standard vaccines rolled out to all pets. 

Sadly though, until more research is available, it’s hard to tell if this will actually help with preventing FISS at all. 

What Else Can I Do?

What is becoming more clear though, is that every cat faces different disease exposure depending on their lifestyle, environment, age and pre-existing health conditions. 

The simplest answer to preventing FISS is that vaccination should be: “performed as often as necessary, but as infrequently as possible.”

Here are some questions I wish I had asked before every vaccination appointment:

  • Can we be sure this vaccine has had a careful assessment that takes into account my cat’s lifestyle? Rather than just an automatic event?
  • Where possible, can this be a single-dose, nasal or topical vaccine?
  • Is the placing of the vaccine in a site that would make tumor removal easier? For example, on the low leg instead of the lower back? Or even on the tail?
  • Is there an oncology department that is linked with this clinic? If so, where can I read about them?

I hope some of this information and insight into our experience helps you or any other pet parent who is going through something similar.

We have had such an outpouring of love and support during this journey. We want to thank you again for staying updated and for supporting Yoda through his treatment! 💖

Please help us share Yoda’s story and help save kitties from the same fate, or send this as a way to support another FISS victim. 

Also, if you would like to contribute to Yoda’s GoFundMe for his treatment costs, here’s the link. We’d so appreciate any support you can afford:

Stay up to date on our Facebook and our Instagram or TikTok for Yoda’s progress and adventures after radiation is complete!


Thursday 6th of April 2023

Lost my beautiful Siamese Lily to FISS ... before I got her she had been vaccinated between her shoulders in Bangkok. The sarcoma developed a few years later after we had moved to the States. (I hadn't vaccinated her again, as she was an indoor-only puss.) The mass came back about a year after surgery -- I hadn't been able to afford radiation -- and then it was very quick. I have a sweet little rescue Siamese snoozing peacefully next to me now, best of luck to you and Yoda from both of us.

The Fluffy Kitty

Thursday 29th of June 2023

Thank you so much, and I'm so sorry to hear about sweet Lily. I wish more vets would educate cat owners before giving them a shot that puts unnecessary risk into their lives, and on our shoulders! thanks for sharing xx


Wednesday 29th of March 2023

Thank you for sharing this. Today, we received the sad news that our kitty, Dibby, has FISS. The situation is remarkably similar to Yoda's - and this truly helped me get through this terrible day.

The Fluffy Kitty

Thursday 29th of June 2023

So sorry to hear this news, Maggie. Much love and light to you and sweet Dibby -- you got this!


Saturday 11th of March 2023

A little late on this but my girl got her vaccinations and rabies. 2 weeks after the vaccinations, I found a lump on her back right leg. I'm absolutely terrified it's this. She's my baby and my emotional support kitty, she's everything to me. I can't imagine having to amputate. It makes me feel like I failed her if she has to go through all this. It breaks my heart having to even take her to the vet. She also has megacolon she's dealing with. With amputation, do they go through depression like humans do? Is it traumatizing to them like it can be to humans? They don't understand why they have 4 legs one day, we take them to the vet, and suddenly they have 3. Do they lose trust in us from this? Dumb questions I know, I just want to protect her and keep her from harm but making medical decisions seems like I'm putting the pain on her and she doesn't know why, even if it'll benefit her in the future. I'm sorry about your kitty. I wonder how he's doing now?

The Fluffy Kitty

Thursday 29th of June 2023

Very valid questions, that I myself asked during the process! Yoda didn't seem depressed at all -- he went about his business as usual, just on 3 lil leggos. It is a very difficult decision, however, and it feels unfair I know. But have strength, because our kitties do! Yoda is THRIVING now, thank you so much for asking! We feel so lucky and blessed he is still with us -- two years later!!

Marianne Johnson

Sunday 24th of July 2022

Think my Jackie has this now….just found it yesterday…..:(

The Fluffy Kitty

Sunday 31st of July 2022

Oh no, we hope not! Is it on the leg? Growing in size?

Deborah Abbott

Wednesday 11th of May 2022

Just wondering how Yoda is doing now ? Our beautiful girl , Paula has FISS also and is due for surgery next week ... best wishes

The Fluffy Kitty

Thursday 12th of May 2022

Hi Deborah -- thank you so much for reaching out! I'm so sorry to hear your Paula will be undergoing surgery as well. We will be thinking about your baby! Yoda is doing fabulous, and I hope that Paula will recover just as well as Yoda did. You'll be astonished at how quickly they adapt to tripod life! Feel free to reach out with questions. You can stay up to date with us by signing up to our newsletter as well. Xx Will be thinking of you & Paula.