Soft tissue sarcomas, AKA spindle cell tumors – why they just kinda suck

Let’s talk tumors, growths, lumps, cancer, whatever you want to call it. And why certain ones suck, but do not suck as bad as others.

There are two broad categories of tumor, based on the cell type from which they originate. Round cell tumors are your lymphomas, mast cells, other tumors whose cells look, well, round when your vet checks them out under a microscope. The name might end in “carcinoma” but doesn’t always. The tumors are the generous types that readily give up cells when your vet asks (usually by poking a needle into the mass). Histiocytomas fall into this category (click here to read about the coolest kind of growth ever!).


The other category of cell type is spindle cells tumors. These are often of connective tissue, such as bones (osteosarcoma), ligaments, blood vessels, and muscle (tumors of the heart). However, spindle cell tumors can appear on the skin of a dog or cat as well, and be rather frustrating. The name of these often ends in “sarcoma.”

What we’re focusing on here are those lumps that pop up on dogs (sometimes cats) that can look like anything. They can be hairless, big, little, and be basically anywhere on the body. They are very frustrating for veterinarians because they are not generous at all with their cells. We can stick a needle into these masses 3-4 times, trying to aspirate out cells for a sample, and get nothing but blood. Not helpful. Yet, we know by process of elimination that if the mass is not sharing its cells with us (clearly they did not watch enough Sesame Street) it most likely is a spindle cell tumor. (The round cell type tumors tend to throw their cells around!)

soft tissue sarcoma, dog cancerMany spindle cell tumors (AKA soft tissue sarcomas) of the skin are not fatal, just annoying. Ideally, we would surgically remove them, just because we don’t want them getting bigger and problematic. And we can’t just cut around the edge, no no! We have to get nice wide margins, meaning we take the tumor’s outline, and add an inch or two all around it. Why is this important? Spindle cell tumors like to extend tiny finger-like projections around the main mass, and we want to make sure we get all of these suckers cut out! If the tumor is on a part of the dog that doesn’t have a lot of extra skin (ie – wrists and ankles) then removing it and getting all of it is practically impossible. In these cases, some people choose to not operate. I get it. These can cause problems depending on how fast they grow, and some may become so large it affects the animal’s mobility. These are, thankfully, the minority.

There are a few different kinds of soft tissue sarcoma. A common one is a hemangiopericytoma, which in vet school we called a peripheral nerve sheath tumor. Other times, we send the lump off to the lab for pathologists to tell us what it is, and all they can tell is the uber-vague “spindle cell tumor” or “soft tissue sarcoma.” Yes, these tumors are highly uncooperative with pathologists as well!

So after all this, why do they only “kinda suck”? Spindle cell tumors rarely metastasize, or spread to other organs and cause major problems. They are what we call “locally invasive,” meaning they stay in one spot. Yes, these tumors do tend to want to come back in the exact same spot they were cut, especially if the vet was unable to get the extra skin around the mass (what we call “wide margins”) due to the location (ie – a foot or leg, where there is not a lot of skin to work with). Many tend to not come back though. And if they do, you know where to expect it!

If your pet has a really persistent spindle cell tumor that comes back, the best way to ensure it will not return again is with radiation therapy. This often involves leaving your pet at a facility to get radiation every day for 3 weeks, and most people (and pets!) don’t dig that. If you happen to live very close to a major specialty hospital that offers radiation, then you are one of the lucky few who can drop off and pick up your pet daily. Otherwise, this option tends to not be realistic for many pet owners.

So yes, soft tissue sarcomas are frustrating to diagnose, and are best treated with surgical removal. Still, as far as cancers go, they aren’t too exciting, because they stay in their place and don’t tend to cause system-wide problems like the bad cancers do. Sure, you might not get an actual diagnosis of the tumor, but you know if it comes back, where it will be (the same place it was!) Kinda like the thief who’s not so smart and rings the doorbell before breaking in the front door. The rate of metastasis is low, making it rarely a fatal cancer.

One exception to this is the sarcomas that occur not on the skin, but deep inside muscle. In this article I’m referring mainly to sarcomas that appear on the surface. It’s possible to have these masses develop in the belly of a muscle, and these are bad news. They are often very painful, and can be very aggressive (particularly in boxers and golden retrievers). While the tumor may not metastasize, these embedded tumors often do shorten a dog’s life, simply because they become so painful the owner elects to have the dog put to sleep. Cancer pain is a whole different type of pain than arthritis, fractures, etc. It tends to not respond to pain medication as well. So even though the tumor does not spread to other organs, its aggressive nature and bad location often does result in euthanasia – to alleviate suffering.

Can these tumors ever spread? It is possible – it is cancer after all, and cancer does not always play by the rules. As far as tumors go, however, soft tissue sarcomas / spindle cell tumors on the surface rank low on the scale of “how likely is this to shorten my pet’s life.”

I’ll take it.

As an aside….In cats, there is a very specific type of spindle cell tumor that is still being studied and hotly debated among specialists. It was once called a “vaxosarc” for “Vaccine-related Sarcoma.” It was thought to arise at places on the body where vaccines were given. Some researchers even went as far as to single out the leukemia vaccine as a suspected culprit, although there is no conclusive proof. These tumors are, thankfully, quite rare, but they are incredibly aggressive and almost always fatal. And, there is currently debate as to whether these rare but super aggressive tumors are related to vaccines specifically, or caused by ANY injection of anything given to the cat. There is much more work to be done on this topic, but I wanted to at least bring it up. For the record, these injection-site related sarcomas, as we are currently calling them, totally and completely suck, unlike the other tumors in this article, which just kinda suck.

Posted in Dermatology, General health, Senior pets.

13 Comments

  1. What is your advice about removal of a spindle cell tumor from a dog who already has cancer?
    Our 10 year old mixed lab was diagnosed with anal sac adenocarcinoma cancer in 2014. Since then she has had 2 surgeries to remove the cancer, 2 rounds of chemotherapy and radiation in January 2017. She currently takes Palladia & Proxicam . Her August CT scan showed the mass treated with radiation, instead of surgery because inoperativ, was non-existent. Which was great news. Now 2 lumps have been diagnosed as spindle cell cancer. Should we put her through surgery again & disrupt her quality of life or leave the lumps alone?

    • Wow! You’ve done a lot, and Anal sac adenocarcinoma is a bad one! Without being her vet, I can’t legally give direct advice. But I can tell you that I myself have asked the question of “how much should I put this dog through?” If I’m not sold on putting them through more, I haven’t. But it never hurts to get the opinion of her oncologist!

  2. Thank you. I appreciate your response. We are always looking at our pets quality of life. We did meet with her Oncologist after I sent in my comment & received more information. She suggests surgery to remove the 2 places because they are very small & on the outside of her body so less invasive. Corona,our dog, has tolerated surgeries very well with no side effects and recover for this will be a week. If we do not remove they could become larger & interfere with other organs. I do dread the day we have to make the decision to not do any more treatments.

  3. Electrochemotherapy is also a good treatment options for soft tissue sarcomas, 9 publications on the subject, please do not hesitate if you want more information.

  4. My 10yr old yorkiepoo has a spindle cell sarcoma high grade on her upper fron limb. The vet recommends amputation. I dont know what to do

  5. Thank you for your article. Our dog has a spindle cell sarcoma on his right leg. They thought it was just a fatty tissue but it grew to a baseball size and is now a grapefruit size swollen with fluid. Surgeon dud a biopsey and didn’t think we should operate due the lack of skin that would remain on his leg and his age being 12. He is fine in every other way but the bump keeps getting larger. No one has a solution to removing the fluid to reduce the swelling and/or pressure. We have his leg wrapped both for support and to keep our dog from licking it.
    Doctors say they’re concerned about infection if they drain it. I’m concerned it will burst open or open up once the skin can’t expand any further on his leg and that will surely cause infection and more. Any recommendations?
    Is the fluid from the lymph nodes? Should the lymph glands be removed to reduce fluid?

    • Without seeing him I’m not helpful. I’m not sure wrapping it is a good idea, as it might be hindering lymph drainage and circulation. Removing the fluid would be fruitless – it would fill back up quickly….and there isn’t much fluid in these, many are solid. Not sure if you are close to one, but a board certified surgery specialist might be a good option for at least a consult.

  6. My 15 year old papillon has a spindle cell carcinoma on his right hip. It’s the size of a small orange after 6 months and inoperatable due to being so vascular, it’s position, size and his age. His appetite is a lot less. I tried to put him on a homeopathic diet, but now he does not like the food. He used to love carrots, now does not. He also tonight started limping on the leg that the mass is on. It feels like the tumour is eating away at his muscle. I’m so worried. I’m going overseas for 9 days at the end of the week, as I am a bridesmaid in a wedding so can’t get out of it. Any idea how fast this is likely to progress in this space of time?

  7. Hello, we have a ten year old miniature poodle who was recently diagnosed with spindle cell cancer, in her case in the lower abdomen. We had the tumor, which was about the size of a golf ball, excised, and a small portion of the lower intestine was excised as well. She’s recovered well, but we’re trying to understand what our best course is moving forward. The biopsy indicated this is an aggressive form of spindle cell, and we don’t know what to anticipate. We need to talk further with our veterinarian, but any perspective you could offer would be greatly appreciated.

  8. Hi. My dog was diagnosed with spindle cell tumor on her paw. Surgery is scheduled next week. There is contradictory article that states this can be ” bad”. That re occurence is 25% and often leads to spreading to other areas. Is your findings up to date? Very concerned for my pet. Any info is greatly appreciated.

  9. Hi,

    I have a 13 year old Bichon Frise who has been diagnosed with a soft tissue sarcoma. She has had two surgeries during the last year. After her first surgery, the lump came back within a month. After her second surgery, she was tumor free for 8 months before it came back. During my most recent trip to her vet, he recommended that we simply monitor her for any changes. My questions are as follows:

    1) What are the changes that her tumor will continue to grow to the point where it breaks through her skin?
    2) The vets recommendation to simply monitor her, is this what is normally recommended given her 2 prior surgeries or is this an outlier?
    3) I understand my pet’s quality of life will decrease as a result of this sarcoma, but can this decrease her lifespan?
    4) what would you recommend?

    Thanks in advance for your help.

    • I can’t offer any specific answers without seeing your pet or being more familiar. That said, if you’re having doubts, seeking a second opinion from a specialist might help put your mind at ease.

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