Monday, May 13, 2013

Cancer in Cats: Fibrosarcoma

Cancer in Cats: Fibrosarcoma

This installment in Old Maid Cat Lady's series on Cancer in Cats for Pet Cancer Awareness Month covers fibrosarcoma. If your cat develops a lump or lesion in an area of the skin, especially if that was the site of a vaccination in past years, it could be cancerous!

What is Feline Fibrosarcoma?

Typically, fibrosarcoma is a cancer affecting your cat's soft tissues, like the skin or connective tissue. It is relatively common. While slow to metastasize to adjacent tissues, it may be quite aggressive locally and can grow rapidly. Some tumors can be more deeply rooted in the underlying tissue.

Three main types of fibrosarcoma have been identified. The first is in older cats, who sometimes will develop an irregularly shaped growth on their body, legs, or ears. Their immune system may be weaker and their metabolic activities may be out of balance, as well. This makes them more susceptible to carcinogens in their environment.

The second is known as vaccine-induced sarcoma, or VAS. More on this below.

The third results from a mutant form of the feline leukemia virus (FeLV). It is the most aggressive of the three and often causes multiple tumors in younger cats.

What Causes Feline Fibrosarcoma?

One cause of this type of cancer in cats is a virus known as the above-mentioned mutation of the FeLV virus, the feline sarcoma virus (FeSV). This type of fibrosarcoma can occur spontaneously.

Another cause of the VAS type of fibrosarcoma is injections. More on this below.

Exposure to radiation can also cause fibrosarcoma, whether through X-rays or from radioactive particles in the air.

What's This About Cancer at an Injection Site?

Some cats have shown a tendency to develop a tumor at the site of a previous injection. Known as vaccine-associated sarcomas (VAS), they could develop anywhere from 2-3 months to 10-11 years after the injection is given. However, they are considered to be extremely rare (1 in 10,000 cats) and the risk of not administering a vaccine is far worse than that of a cat developing a sarcoma. 99% of cats who get vaccinated never develop a VAS.

VASs typically grow in the connective tissue between the skin and muscle. They were discovered in 1991 at the University of Pennsylvania School of Medicine. First associated with rabies vaccines, they were soon found in cats who had been vaccinated against feline leukemia virus, panleukopenia, and rhinotracheitis. Some studies are focusing on the inflammation caused by vaccinations, to which some cats are more susceptible regardless of the type of vaccine being given.

The role vaccinations play in causing these sarcomas is not really proven. There seems to be more of an incidence when killed-virus vaccines are used. This is hypothesized to be due to the addition of a "booster" known as an adjuvant that is added to killed-virus vaccines to help stimulate the immune system and make the vaccine more effective. Vaccines containing aluminum as an adjuvant have been shown to produce more inflammation (swelling) at the injection site after they have been given, and this factor has been shown to increase the risk of the cat developing a VAS.

Most VASs occur in the shoulder or the rear haunch area, which are common locations for these injections to be given. Fibrosarcomas likely resulting from vaccines have a tendency to be more aggressive and more malignant than those resulting from other causes.

Studies continue on the relationship between vaccines and fibrosarcomas in cats. Some cats have also developed five other types of tumors at vaccine injection sites. As many as six different types of tumors have been observed affecting the muscle, bone, cartilage, or fat at injection sites. Different methods of administering vaccines are being explored to completely eliminate this risk.

Our feline companions are considered to be more at risk for VASs than are other types of pets because cats have a higher sensitivity to chemicals that have their oxidation status changed (oxidative injuries). These substances include onions and acetaminophen, both of which are harmful to cats. Their susceptibility to this condition likely increases cats' risk of developing a VAS in vaccines containing aluminum.

What Symptoms May Indicate Fibrosarcoma?

You would likely first notice a lump or lesion that appears to be just underneath your cat's skin. It could be on the head, body, or legs...or even in the mouth. Oral sarcomas are the second most common type of oral cancers in cats.

The lesion may just appear as an area of swelling, and could be fleshy or firm. It may not be painful for your cat. The lump is often irregular in shape. Sometimes it looks ulcerated, in which case it has probably been there longer. If such a lump does not go away after about 3 months, if it is more than  3/4" across, or has increased in size, a biopsy is warranted.

Fibrosarcomas can also develop inside the cat's body, typically in the connective tissue in the ribs, pelvis, spine, or head areas. This tissue connects the body's bones to the muscles. In these locations, likely because it takes longer to discover, the cancer has a lower survival rate than those found near the skin.

If left untreated or undiscovered until the cancer has advanced, the cat may have difficulty chewing or eating, lose his appetite, get dehydrated, appear to be in pain when walking, become lethargic, or have unexplained bleeding from the mouth. Some may have a bad odor in the mouth, if this is the location of the tumor. By the time these symptoms develop, the cancer is likely quite advanced.

How Can I Be Sure It's Fibrosarcoma?

If you discover such a lesion on your cat, get thee (and thy cat) to the veterinarian!

Your veterinarian will do a thorough physical examination, blood testing, biochemical profile, urinalysis, a tumor biopsy, and X-ray of the tumor site to determine its size, and possibly a chest X-ray to see if the cancer has metastasized. The biopsy will tell the doctor whether this is a fibrosarcoma or an osteosarcoma, which has a different course of treatment.

What is the Treatment for Fibrosarcoma?

The first thing is to surgically remove the tumor. This will likely also include a margin of adjacent tissue, since these tumors are so locally aggressive. They have tiny, microscopic cells that extend like little fingers or tendrils into the tissue surrounding them, so it's very difficult to remove all of it. If it's on a limb, the tumor will likely cause the cat to lose that limb to surgery. Most recover and function just fine with three legs, and many cats have even lived a happy life and learned to adapt with only two! Obviously, younger cats are better surgical candidates, as older cats can have issues with anesthesia. Yes, this is some serious, major surgery. If possible, have it done by a surgeon who specializes in it, rather than at your local vet's office.

Some states are now experimenting with a vaccine against fibrosarcoma that can be given at the time of surgery to decrease chances of a recurrence. Because it is only experimental, the USDA prevents its being given to cats who have not already had a fibrosarcoma. As of 2012, this vaccine was only available in Arizona, Florida, Georgia, New York, North Carolina, and Tennessee.

Radiation therapy may also be performed both before and after surgery to minimize chances of recurrence and reduce the pain for your cat. It kills any residual cancer cells remaining after surgery, as it is difficult for a surgeon to remove all of them. The best outcomes are when radiation is given before surgery and when the tumor can be cleanly removed during surgery. When administered after surgery, radiation can cause the surgical wound to heal more slowly. The cat's hair near the incision may also grow back in a different color, usually gray or white.

Chemotherapy for fibrosarcoma in cats is actually also very effective, especially in cases where the cancer has metastasized (spread). The chemo is typically administered to the cat four or five times, every few weeks for about 90 minutes per treatment. Sometimes it can be injected at the time of surgery to kill any cells that were missed in the surrounding tissue. Chemo is very physically tiring for the cat and rough on the body, so most vets consider it the option of last resort. Your cat will probably also be prescribed something to relieve pain.

Treatment is generally very effective at fighting this type of cancer in cats, with most patients still in remission two to three years later. However, fibrosarcoma also often returns, so once a cat has been diagnosed with it, more frequent visits to the vet are recommended. Subsequent vaccination sites should be closely monitored to make sure another sarcoma does not develop there.

A diagnosis of fibrosarcoma is not an automatic death sentence for your cat; many cats live long and happy lives after the cancer is removed. But as with all cancers, it must be caught early and treated, or it could become life threatening. The chance of a fibrosarcoma spreading to the major organs is only 3%-5% if caught early. But if it goes untreated, that risk rises to 24%. Younger cats also stand a better chance of recovery than older ones.

Is There Any Way To Prevent Fibrosarcoma?

When it comes to the VAS type of fibrosarcoma, yes! Cats only really need one annual vaccination, and that's for rabies. The others are not necessary. Less injections mean less injection sites, so less risk for the inflammation that can lead to a VAS. Have your veterinarian run a blood titer to determine your cat's immunity level before automatically getting vaccinations for everything every year. Then you can only have your vet give vaccines for those where kitty's immunity has fallen low.

Next, when getting your cat's vaccinations, request a recombinant rabies vaccine rather than an inactivated one. And make sure that any vaccines your vet is using are non-adjuvanted. These typically must be given more frequently, but are less likely to cause the inflammation around the injection site that is associated with VASs.

Make sure that the needle your vet is using on your cat is no larger than 25 gauge. Dogs may be able to handle larger needles, but the smaller ones will cause less irritation for a cat, as they will carry less debris and hair with them under the skin. You may also request a vaccine that is administered intra-nasally. There are newer vaccines on the market now that require no injection at all. These present the least risk for VASs and would be especially important to use on cats that have previously been treated for a VAS. If your cat needs another type of medication that can be given orally rather than by injection, opt for that. No, it's not fun to give a cat a pill, but it's far better than putting your cat through expensive and dangerous surgery, radiation, and chemo!

Massaging the area where the vaccine was given may also help by spreading out the material injected into the body. This must be done just after the shot is given. And make sure your vet keeps detailed records on the brands of vaccines used and the sites at which they were injected into your cat. This can be very helpful if you detect a lump that requires further investigation.


  1. Vixen is beautiful! My siamese cat Mocha lived to be 20 before she had to be put to sleep due to old age related disease that left her emaciated, unable to eat or get around very well. She was a baby and I miss her. Now I have a female siamese 'Cocoa" just over a year old who 12 days ago received the core vaccine a year after having received it(requested by our vet) and a lump about 3/4 of an inch has risen near the base of her back right side , beside her spine. I'm hoping it will go away as I'm reading about VAS. Most sites say that if the lump does not go away from 1-4 months I should be concerned. However right now I'm starting to worry. I'm crossing my fingers all is well and the lump will shrink to nothing.

  2. Thanks for your comments, David! LIttle Vixen made it to age 24, and I just lost her last year, which was devastating. An oil portrait of her hangs on my dining room wall, and I now share my life with two red mackerel tabbies I started fostering as 4-week-old kittens just two weeks after Vixen's death. I hope your Cocoa will be okay! Not familiar with the core vaccine.

  3. My sweet kitty is going in tomorrow for his third surgery to remove new tumors that recurred 2 months after his last surgery. It seems we will be chasing these and removing for a while but my hope is that catching them early will prevent metastasizing to his organs.

  4. Sound therapy is popularizing these days because it is a very efficient and 100% natural therapy which has no side effects. Sound therapy can not only be used in such cases but can heal Cancer fibrosarcoma. There is no doubt the power of Sound Healing and positive thinking is astonishing.

  5. my 18 year old tabby developed a lump a litter bigger that a marble on her front right paw in the area that would be considered our wrist area. This lump appeared over night. I took her to vet on Sunday and they did a biopsy and said it was feline fibrosarcoma and becasue she was 18 with a level 3 heart murmur and early stage kidney diease she was not a candidate for surgery or chemo. I got a 2nd opinion and this vet said we could try to remove the lump but likely would have to amputate her leg. At 18 I feel like this would be extremely cruel. The 2nd vet said even if he did surgery and followed with radiation she would likely get another tumor and likely not live very long. Is just radiation to keep the tumer small a possibility? In 1 week it has grown and is starting to wrap around her paw. So far she isnot in pain but I am lost as to what to do. I want what is best for her. Any suggestions or opinions are welcomed. Thank you. JoAnne Charlotte NC

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  7. My 18-year old tabby has developed a sarcoma on her head near her ear. At her age, we would not even consider surgery. What will be the sign(s) that the end is near, so that we might humanely have her put to sleep?

    1. Hi, Madeleine,
      I'm so sorry to hear about your kitty. Your vet should be able to tell you how severe her sarcoma has gotten, and how it should progress if left untreated.

      I'm not a veterinarian, so can't really say other than with my own experience in losing cats. My vet's office manager told me I'd know when the time was right when my first cat was nearing the end due to kidney failure. I couldn't see ever getting there, but when he finally lost control of his bladder and seemed to be suffering more, I knew it was time. Our poor little Frankie had FIP and I should have let him go when the final stage appeared, but couldn't bear to do so. He was hospitalized at an emergency vet overnight, then came home for one night before going to his regular vet that Monday morning, where he remained until his death a week later. I should not have put him through that additional week of suffering. With little Vixen, she died naturally at home at age 24. It was difficult to go through, but she was no more in pain than she had been in the last few years of her life due to arthritis, and I knew she didn't want to leave me one moment before she had to. She died in her sleep, in her bed right by the head of where I was sleeping on the sofa. For all of them it was different, but each cat is unique. You will know when your cat is at the point where ending her life is a better choice than continuing on. Rely on your vet's advice and your own intuition.

  8. Our good kitty Gretchen had fibrosarcoma. I discovered the first tumor when it was a bit bigger than a grain of rice. Each time we removed a tumor, more appeared. She had three surgeries before we decided to let nature take its course. She lived about a year after the last surgery. We believe she was about 16or 17 when she died. This is how that played out. She spent a very pleasant Saturday sleeping in the sun on our balcony and visiting all her old haunts around the house. Very early Sunday morning, she was taken with seizures, and died three hours later, at the emergency vet's office in my arms in the car in the parking lot. Would I do it again? I don't know.

  9. My sweet Collette is only about 7 years old. Her first surgery on her upper right thigh was one year ago today. The chemo and radiation afterwards for her was out of the question due to cost. AND there are no clear cut facts that those therapies would work, considering the depth of the tumor. There were no other options for her. Her second tumor developed a month later. I delayed surgery as I was hoping that nature would take its course-it didn't. Her second surgery was this past June 2015. She was put on Kinavet and it did help control the growth for two months. In Mid-September the tumor regrew. She now has trouble walking and cannot really use her right leg as the tumor is very large. I love her -has been my "Velcro" cat ever since I adopted her. My decision to euthanize her is so difficult for me, but her pain and increased immobility is making me more aware that she needs to die with the dignity and grace she deserves.

  10. I'm owner of a cat that is a VAS survivor for 6 years now.
    At 8 she had a small lump between her shoulder blades, and she had surgery the same day of the diagnosis. It was a small tumor, with two roots (the most developed was growing parallel to the spine and didn't connected to anything, the other was growing toward the spine and just connected muscle tissue. the tumor hadn't blood in it, but it was G2. She had no other treatments. Luckily there were no recurrence. Here a video of two weeks after surgery
    She's almos 15 now, a senior.

    Not all cats develop VAS, but since it happened to my cat, I have chose to not vaccinate my younger cat, unless is necessary. And when she need injection (maybe antibiotics, it happened once), I ask to vet to shot her in the legs, just in case.

    1. Your comment gives me so much hope. Our 9 year-old cat will go through surgery for a very similar tumor next Tuesday.
      It's 1.9cm diameter in the biggest place and it doesn't seem to have expand beyond what we can see in the CT Scan.
      One round of radiation right after the surgery will be applied while waiting for the results of the test of the tumor.
      We were second guessing going through this with her because of her age. We don't want to put her through that for our selfishness. But today our regular vet told us we are not persuing "delaying death" but because it was caught at an early stage we are persuing the total healing.
      Your comment made me hope.
      Thank you for sharing.

  11. We have a 14 year old diabetic female cat ( 6 units of insulin twice daily) and we found a lump on her front leg on the "elbow" vet took sample by needle to send off and we found out today that it is sarcoma :'( We don't want to put her through a surgery and take her leg. What is prognosis for a healthy albeit diabetic cat with untreated sarcoma? We don't want her to suffer and she still runs through the house and plays like a kitten.

  12. My Jazzy is 19 today. She was diagnosed with Fibrosarcoma last November 2015 with the first lump appearing on her right shoulder blade. The vet said she was too old to undergo surgery & this cancer is very aggressive. Even if we removed the tumor, the cancer shoots off tentacles causing more tumors to grow all over the body. She was not in any pain & as the months have passed, another tumor formed below the primary tumor. 2-1/2 weeks ago, the tumors ulcerated (opened up). My vet had warned me this was not a pretty sight & most people put their pets to sleep at this point. I have opted to nurse her woulds with a product called MediHoney (found on Amazon). Bacteria will not grow on honey! I use a mixture of MediHoney & Neosporin on gauze (liberally) and place it over the wounds. I keep them in place with gauze bandage wrap around her body & over her shoulders to keep the wrap in place. I then place a stocking over the area to keep the gauze from being scratched open (she tries to itch them). I also put her on a week of oral antibiotics immediately when the tumors opened to prevent a secondary infection. The bandages are changed twice a day. I've just started her 2 days ago on a low dose pain medication Buprenex from my vet to keep her comfortable. She's still eating, drinking, walking all over the place, grooming & using the litter box. Yes, I know she's dying and my time with her is short now that the tumors have opened. Today (May 15, 2016) is her 19th birthday. I just lost my dog of 16-1/2 years 5 weeks ago after an apparent stroke, seizures & he died in my arms at home. These are the last of my fur babies & I'm a very attentive "mom". I would do anything for them & have. I don't know how long Jazzy has, but she's survived 6 months after being diagnosed. My loving care of her tumors doesn't bother me whatsoever & I do it out of love. She's not ready to be put to sleep, just because of a wound. I will know when her time comes to say goodbye, but it's not today. Happy 19th Birthday my Jazzy! xoxo

    1. How is Jazzy? My cat has an ulcerated fibrosarcoma but still acts normally eating and drinking. I am giving her pain medication from the vet though she doesn't seem to be in much pain. I know that she we go soon but I am wondering how long she has now that the tumors are beginning to ulcerate.

    2. How is Jazzy? My cat has an ulcerated fibrosarcoma but still acts normally eating and drinking. I am giving her pain medication from the vet though she doesn't seem to be in much pain. I know that she we go soon but I am wondering how long she has now that the tumors are beginning to ulcerate.

  13. My 16 year old kitty, Sweet Pea recently developed a small irregular mass below her shoulder. The vet is 99% sure it is cancer and does not recommend surgery as she also has some pretty bad arthritis and just hurt her leg too. To top it off less than a year ago she had a significant surgery on her mouth due to stomatitis. I can't remember what type the vet said except it is some kind of sarcoma. That appointment was a total blur. I am noticing the lump getting smaller. I'm wondering if sarcomas ever get smaller or perhaps she has something else and was misdiagnosed? What do y'all think?

    1. It could be inflammation - which is what my vet was hoping my kitty's lump was - it was not. However b'c your kitties tumor is getting smaller is hopeful, you can talk to your vet about doing an aspirate - which is a needle biopsy that could be done with local anesthetic.

  14. Thank you for all your stories, my kitty Cracker had a large tumor on his back just removed two days ago and pathology showed fibrosarcoma. I am heartened to see that some of your babies have lived a long life after diagnosis. I am going to try acupuncture and alternative therapies - any recommendations on treatment (dont want radical surgery) would be appreciated.

  15. Our 10 year old manx was diagnosed with soft tissue sarcoma today. She had surgery last Friday and is recovering pretty well. We've decided not to put her through an amputation or chemo. We want her to have a good quality of life for as long as possible. Our vet will not give me a prognosis. The closest oncologist is 2 hours away and will not speak to me by telephone unless we meet with her in person even though she has all of the pathology reports. Have any of you ever tried Life Gold? It's a cancer support med for cats.

  16. Helpful. I'm a vet tech and have an old kitty with was.

  17. Helpful. I'm a vet tech and have an old kitty with was.