Fibrosarcoma in Dogs: The Definitive Guide to Understanding Your Dog’s Cancer (2020)

By Vicki Andersen

Happy dogs
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Fibrosarcoma. Cancer. Two words that no dog owner ever wants to hear. How can this be happening to your beloved canine companion?

Will my dog survive? How long will he or she be with us? Will they suffer? Are there treatments I can afford? Are they painful? These thoughts might race through your mind immediately after hearing the vet say “it’s fibrosarcoma.”

Before the panic sets in, it’s important to understand what fibrosarcoma is, the differences between fibrosarcoma and oral fibrosarcoma, and the various treatments available.

Years ago, hearing the word fibrosarcoma, or soft tissue cancer, for any dog meant a short time of survival, several months at best. Today, median survival times continue to improve with treatments. And more importantly, during these treatments, they can live quality lives filled with joy.

Each dog’s experience will be different, but there is information to help guide both your dog and your family through this time. Let’s take a deep breath and explore just what fibrosarcoma and oral fibrosarcoma are and what can be done for your dog once you’ve heard this diagnosis from your vet.

Fibrosarcoma in Dogs

fibrosarcoma cells under a microscope
Fibrosarcoma cells under the microscope. (Image purchased from Adobe Stock)

What is fibrosarcoma? A fibrosarcoma tumor is a type of soft tissue cancer usually found in the connective tissue on the limbs and trunk of the dog’s body.

Connective tissue connects and supports other tissues and organs in the body. Fibroblasts are the cells that maintain the structural integrity of the connective tissues. If they suddenly grow uncontrolled in the body, they can create a tumor called a fibrosarcoma.

The good news is that fibrosarcomas can be removed via surgery. They often do regrow after removal but many are slow to metastasize or spread to other parts of the body.

Oral Fibrosarcomas in Dogs

Oral fibrosarcoma tumors behave differently than regular fibrosarcomas. They can occur on the gums, the upper and lower jaws or the roof of the mouth and sometimes even on the tongue. They can sometimes invade the dog’s jawbones. Unlike other fibrosarcomas, oral fibrosarcomas grow rapidly.

Oral fibrosarcomas represent between 17% to 26% of all mouth tumors in dogs. About 25% are found in dogs less than five years old and bigger dogs are more likely to develop them than smaller breeds. They are also more commonly found in male dogs than in females.

Is Fibrosarcoma Hereditary?

Is fibrosarcoma a hereditary disease? Strand of DNA helix
Is fibrosarcoma a hereditary disease? (Image purchased from Adobe Stock)

Usually, large breed dogs are at a greater risk than small breeds to develop fibrosarcomas. They are more common in older dogs. The average age to develop fibrosarcoma is about 10 years old. Some breeds are more genetically disposed to it than others, including Golden Retrievers, Doberman Pinschers, Irish Wolfhounds, Brittany Spaniels, and Gordon Setters.

What Does a Fibrosarcoma Look Like on a Dog?

A fibrosarcoma between a dog’s front toes on its paw
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Two fibrosarcomas: one between the toes, one above the hock

A large fibrosarcoma tumor on a dog’s back leg just above the hock
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Fibrosarcomas can look differently depending on where they are found, how far they have progressed, and their size. They usually look like a bump or a lump under the skin. They may look like benign fatty bumps and tumors called hemangiomas. Sometimes fibrosarcomas may open and bleed, and become infected, but not always. They may not be noticed until they are pretty big, depending upon where they are located on your dog’s body.

What Does Oral Fibrosarcoma Look Like on a Dog?

a large oral fibrosarcoma on a beagle’s face
Oral fibrosarcoma on a beagle. (Image purchased from Adobe Stock)

Oral fibrosarcomas usually look like a swelling on the gums by the teeth. Oral fibrosarcomas will usually break open and bleed and can cause bad breath. The tumors can go deeper than what you might physically see and some can invade the jawbones.

Every dog will be different, but signs that your dog might have an oral fibrosarcoma include: swelling or pain in their mouth, difficulty eating, their teeth may shift in the mouth or there may be facial swelling also. They may have excessive drooling and panting too.

Only about a third of oral fibrosarcomas will spread or metastasize to other parts of the dog’s body.

What Causes Fibrosarcoma and Oral Fibrosarcoma in Dogs?

A post it note with the word WHY? Why fibrosarcoma
(Image owned and created by Vicki Andersen)

It’s unknown what causes canine fibrosarcoma or any canine cancers, but there are many theories and ideas about what may influence them to form.

Infections and exposure to chemicals may play a part as well as the predisposition of some breeds. Many vets, both traditional western medicine and holistic practitioners, say that canine diets have changed, moving away from the wild dog’s natural raw diet and moving towards more processed foods. These processed foods may contribute to an increased amount of cancer in our beloved dogs. But there really are no scientific studies to definitively say what causes fibrosarcomas and oral fibrosarcomas in dogs.

How is Fibrosarcoma in Dogs Diagnosed?

When you visit your vet, they will want to know approximately how long the growth has been there, if its shape has changed, and if it has impacted your dog’s behavior, i.e. changes in eating, sleeping, walking, or playing.

Sample tissue from the tumor has to be taken in order to make a definitive diagnosis.

What is Fine Needle Aspiration?

Fine needle aspirate being fixed onto a slide in a lab.
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Fine needle aspirate being prepared for a slide

Fine needle aspiration involves taking a small needle and inserting it into the tumor to withdraw cells that are then examined under a microscope by a veterinary pathologist. This is called cytology. However, a fine needle aspirate on a fibrosarcoma may not yield a definitive diagnosis of fibrosarcoma because it does not collect enough tissue material to make a decision. Vets generally prefer an excisional tissue biopsy to diagnose fibrosarcomas definitively.

Excisional Biopsies: The Gold Standard for Diagnosing Fibrosarcoma?

Removing some of the tissue from the tumor is called an excisional biopsy or debulking the tumor. This procedure is done under anesthesia at the vet’s office. The vet then sends the tissue sample collected to a veterinary pathologist. This is called histopathology. Vets prefer using excisional biopsies to diagnose fibrosarcoma.

Surgery to Remove Fibrosarcoma Tumors

Once the diagnosis of fibrosarcoma has been made, it’s time to schedule surgery to remove as much of the tumor as possible. Surgery alone may not be enough to combat the cancer, but without surgery, radiation and chemotherapy are not enough to kill the fibrosarcoma tissue.

Complete surgical removal of fibrosarcoma tumors is difficult because of the way they grow. The tumors often send out finger-like tentacles and removing all of the tumor, when it may be only microscopic and not easily seen by the surgeon, is nearly impossible.

Once the surgery is complete, and the healing process is underway, consultation with your veterinarian is important to determine what the next steps in your dog’s cancer journey might be.

Next Steps in the canine fibrosarcoma journey.
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It’s Out, Now What?

A dog’s left flank post surgery with sutures and staples.
(Image owned and created by Vicki Andersen)

Post fibrosarcoma removal: surgery site with sutures and staples

After removal, samples of the fibrosarcoma’s tissue are taken and sent to a veterinary pathologist who examines the cells under a microscope to find the type and grade of the cancer. Knowing this information will help inform your choices for treatment.

Tumors can be graded as low or high, all depending upon how fast the cells are dividing. Bloodwork, X-rays, urinalysis, and ultrasound can also be used to check if the cancer has spread to other areas.

In oral fibrosarcomas, if the tumor is invasive into the bones of the mouth, the surgery may involve removing a portion of your dog’s jaw. Removing parts of the jaw can provide pain relief for your dog.

For dogs with oral fibrosarcomas, the vet may also do a fine needle aspiration of lymph nodes under the chin if they look enlarged or feel abnormal to see if there has been spread.

What to Expect After Fibrosarcoma Removal

Fibrosarcomas are likely to regrow, usually within one year. But even though there is no cure for either fibrosarcomas or oral fibrosarcomas, your dog can still have a great quality of life after tumor removal. Tumor sites should be monitored after removal to look for signs of regrowth and if it is noted, see your veterinarian right away. Fibrosarcomas tend to recur, usually in the same area, which is why closely monitoring the site is important.

Unfortunately, this fibrosarcoma regrew after 3 months. (Image owned and created by Vicki Andersen)

Can It Be Cured?

Since it’s not possible for the veterinary surgeon to always see the tendrils that grow out from the fibrosarcomas, vets assume some microscopic bits of the tumor will remain even after surgery, which is why the tumors are able to regrow.

Effective Treatments for Fibrosarcoma

Surgery remains the best course of action to remove the fibrosarcoma, whether oral or on a limb. Some surgeries on oral fibrosarcomas may be radical or may not be able to achieve full removal of the tumor. Post-surgical radiation or chemotherapy gives the dog the best chance at a longer time without regrowth of the fibrosarcoma.

Radiation for Fibrosarcoma

Radiation table for treatment.
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Surgery is the best course of action, followed by radiation if the dog can tolerate it. Radiation can help shrink whatever remaining cancer tissue is left behind. Up to 40% of tumors without complete removal and without radiation regrow. With surgery and radiation, dogs have a five-year survival rate of greater than 75% and a regrowth rate of around 16%. But radiation isn’t for every dog or family.

Radiation involves full anesthesia because the animal needs to remain still during the treatment. It also requires multiple treatments, which can become costly, in excess of several thousand dollars. Radiation treatment can be harder on older dogs since it involves weeks of daily treatment, each treatment requiring daily anesthesia and recovery time. Radiation can help your dog achieve many happy fibrosarcoma-free years.

Speaking with your veterinarian and asking questions about your particular dog is important when making the decision on whether or not to proceed with radiation.

Chemotherapy to Slow Tumor Regrowth

Chemotherapy drugs for canine fibrosarcoma
Chemotherapy drugs for canine fibrosarcoma. (Image owned and created by Vicki Andersen)

If radiation is not for your dog or your family, it may be possible to try chemotherapy. Once the majority of the fibrosarcoma has been removed, your vet may recommend chemotherapy to slow the tumor’s regrowth while keeping the dog comfortable. Chemotherapy can consist of one drug or a combination of drugs given orally or intravenously. Usually, it is given with Rimadyl for pain relief. The cost of chemotherapy varies depending upon the drug or drugs used. Most dogs tolerate chemotherapy well and it does not cause the side effects we think of with human chemotherapy.

While on a chemotherapy regimen, your vet will check your dog’s blood work periodically to ensure there is no lasting damage being done to their liver or kidneys. Additionally, the vet will see your dog every four to eight weeks to check for any changes in body weight, appetite, stool, activity, or hair loss. Sudden changes should be reported to the vet immediately.

New Directions — Genetic Tumor Testing

DNA helix graphic
DNA helix (Image purchased from Adobe Stock)

It used to be that genetic tumor testing was just for humans. As of 2020, it is possible to have your dog’s tumor tested to see if there are any compatible drugs based upon the DNA of the tumor that can help slow the tumor’s regrowth. During this testing, DNA is extracted from the tumor’s tissue sample and using genomics, it is possible to see if there is a mutation that can benefit from existing chemotherapy drugs. With a price tag of $1,000, it is an expensive DNA test, but many dog owners are willing to pay to see if targeted therapy can work for their dogs.

The best course of action is to consult with a board-certified veterinary oncologist if possible. They can layout the options, benefits, and risks of the various treatments for your dog.

Natural Treatment for Fibrosarcoma in Dogs

natural canine raw diet foods
Natural canine raw diet foods. (Image purchased from Adobe Stock)

Homeopathic vets believe in supporting the dog’s whole body health through nutrition and some homeopathic medicines. They recommend changing the dog’s diet to fresh, homemade ingredients and supporting the dog with nutritional supplements.

How Long Can Dogs Live with Fibrosarcoma?

Each individual dog is different depending upon the grade of the tumor and how advanced the cancer is. There is no general time frame because it is so dependent upon the grade and size of the tumor. Your vet will be able to give you the best prognosis for your individual dog.

Life Expectancy for Dogs with Oral Fibrosarcoma

For dogs with oral fibrosarcoma, the prognosis is more guarded. Some dogs who undergo radical surgery to remove the tumor and jawbone pieces can survive as long as two and a half years. The median survival time is seven months with half the cases surviving beyond one year. According to veterinarians, fibrosarcomas located closer to the front of the mouth are usually easier to treat, so they have a better prognosis. Consultation with your vet will give you the best survival timeframe for your individual dog.

Happy dog face with tongue out
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Fibrosarcoma and Your Dog’s Future

When you first receive the diagnosis of fibrosarcoma, panic is the natural reaction along with fear about what comes next. You don’t want to lose your dog and you worry for his or her quality of life.

Knowledge is power and having a better understanding of what fibrosarcoma is and knowing that there are options can lessen your anxiety. Take a deep breath and start asking your veterinarian questions about your dog’s specific needs and situation. Hopefully, there are solutions that will be right for both your dog and your family.

woman hugging her older golden retriever in front of a window
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Fibrosarcoma doesn’t have to be an immediate death sentence. There are proven treatments available to give your dog quality of life in the time remaining — hope should never be lost!

man high fiving a yellow lab — hope for the future.
Hope should never be lost! (Image purchased from Adobe Stock)

Vicki Andersen is an SEO content marketing writer. More of her work can be found at or at and on Medium.

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