Fibrosarcoma in Cats and Dogs Causes, Symptoms, and Treatment Options for Fibrosarcoma

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Fibrosarcoma is a form of cancer that is most commonly found in the skin and soft tissue of dogs and cats. Find out more here in order to better understand this particular form of cancer and what options are available.

Fibrosarcoma ... It even sounds unpleasant, doesn’t it? With the root ‘sarcoma’ you know it’s a cancer, but what exactly is fibrosarcoma?

Fibrosarcoma is a cancer that appears in the skin and soft connective tissues of both cats and dogs. Fibrosarcoma in cats is often found between the shoulder blades, on the back of the neck, and on the chest. Fibrosarcoma in dogs is often found in the mouth, particularly the jaw, and on the limbs. In rare cases though, the cancer can be found in the bones of both animals.

The tumors vary in growth rate between cats and dogs and from breed to breed. Prognosis varies as well depending on the location and size of the tumor, as well as the age and overall health of the animal.

Causes of Fibrosarcoma

While we know that fibrosarcoma is a cancer that originates in the soft tissue, no one knows for sure what exactly causes the fibroblast cells of this tissue to divide so abnormally and quickly. Here are the theories.

In cats, some researchers have linked fibrosarcoma to recombinant forms of the feline leukemia virus, especially in young cats, as well as cats older than 5 years of age who exhibit multiple tumors. Other researchers have turned their attention to vaccinations, stressing that the tumors commonly appear at the injection site -- the shoulders and neck. However, traces of virus particles from the vaccinations have not been found in the tumors.

A subtype of fibrosarcoma, feline sarcoid, is thought to be caused by a papilloma virus, which is responsible for wart growth.

In dogs, the theories are few and far between, but researchers have found fibrosarcoma to be more common in larger breeds of dog, especially those who are 10 years of age and older. However, serious cases with poor prognosis have been seen in dogs younger than 1 year.

Fibrosarcoma Symptoms

The most common and apparent symptom of fibrosarcoma in cats and dogs is a lump, which at times may be accompanied by ulceration and bleeding. Other common symptoms include swelling of the affected area and pain when the area is touched. You may find that your pet becomes less social, refuses to be touched, and experiences a loss of appetite due to the resulting pain. If the tumor appears on the legs, related symptoms include loss of motion and an inability to walk.

When in the bone, fractures may occur even if there has not been an incident of physical trauma.

Fibrosarcoma Diagnosis

Fibrosarcoma in both cats and dogs is commonly spotted during a physical examination. If your veterinarian comes across a lump he or she believes to be a tumor, they will review your pet’s health history and ask questions regarding onset of symptoms, as well as any out of the ordinary incidents, such as accidents or illnesses. They’ll then call for laboratory tests including a urinalysis and blood work. If symptoms point to possible fibrosarcoma of the bone, x-rays are administered and occasionally a CT scan. A biopsy of the tumor is then taken to determine if it is benign or malignant.

Fibrosarcoma Treatments

Since fibrosarcoma does not respond well to radiotherapy or chemotherapy, surgical removal of a tumor is often recommended. During removal, the veterinarian typically extracts excess tissue around the tumor to be certain it is completely removed.

Until the procedure is performed you will need to focus on everyday treatment of the existing tumor. This includes preventing your pet from rubbing, scratching, licking or biting the tumor, as well as keeping the area clean, especially if the tumor has become ulcerated.

Post surgery, your pet will need a lot of rest and some special care:

  • If possible, set up a special spot in a quiet, temperature-controlled area of your home.
  • Your pet will also be in a lot of discomfort, so pain medication may be prescribed.
  • Be sure to follow all directions to avoid a possible overdose.
  • The resulting pain may also affect your pet’s eating habits, causing them to eat less.
  • Monitoring their water and food intake can help avoid dehydration or malnourishment during the healing process.

If your pet isn’t eating, the vet may recommend specific foods and nutritional supplements.
You’ll want to keep your pet from rubbing, scratching, licking, or biting the incision site.
Of course, keep the area clean to prevent infection.

If the fibrosarcoma is found within the bone, the surgical approach is typically more aggressive, and removing part of or the entire bone may be required. Post-surgery treatment will vary.

Follow up visits to the vet to regularly monitor for any re-growth of the tumor or spread of the fibrosarcoma are necessary, but the good news is a full recovery is possible. 

How Long Will a Cat Live with Fibrosarcoma?

Since fibrosarcoma is a type of cancer, the lifespan of a cat with it will vary depending on how severe the condition is. Sadly, fibrosarcomas can sometimes be very aggressive and grow rapidly. Treatment almost always involves surgical removal and chemotherapy. Grade 1 and Grade 2 tumors grow slowly, but leaving them untreated is not a good idea. Grade 3 tumors are very aggressive and spread fast, requiring immediate intervention. According to Long Island Veterinary Specialists, if your cat has high-grade tumors but receives a battery of treatment options, including surgery, radiation therapy, and chemotherapy, your cat may have a 50% chance of living for another two years. This type of battery is needed because, with only surgical removal, the cancer tends to return within weeks or months. Radiation therapy and chemotherapy help keep remission away for even years. 

What Causes Fibrosarcoma in Cats?

Firstly, we have factors that make cats more prone to this condition. Middle-aged and older cats tend to see more cases than younger cats. Similarly, breeds like Siamese and Himalayan cats also seem to have a higher risk of developing fibrosarcoma. Vaccination is one factor that seems to be related to cases of fibrosarcoma. A tumor can start to develop at the vaccination site, especially if the vaccine contains ‘adjuvants.’ This refers to components that aim to improve a vaccine’s effectiveness. Fibrosarcomas can also develop due to foreign bodies that get stuck under your cat’s skin. This can lead to inflammation, which might lead to fibrosarcoma. In rare cases, the causal factor might also be linked to the Feline sarcoma virus (FeSV). It is fast-growing and tends to affect younger cats with Feline Leukemia Virus (FeLV). 

Is Fibrosarcoma Painful in Cats?

As far as the actual tumors are concerned, no, they aren't directly painful. Grade 1 and grade 2 tumors are generally painless. That said, they can grow to such a size that it makes life uncomfortable for cats, depending on the region of the tumor. If tumors develop near the mouth or on the gums, it can prevent eating and drinking, which can be highly stressful for the cat. According to Dr. Tammy Hunter, DVM, oral pain can occur, especially when the tumor penetrates the underlying bone. However, tumors on the tail are out of the way, and for the most part, the cat can live without hindrance. If the tumors are left unchecked and grow to such an extent that they stretch the skin and even break open, this can be painful. It can become a source of secondary infection. Vets may recommend painkillers in these situations. But ideally, you want to avoid letting it worsen to such a level. 

What Does Fibrosarcoma Look Like in Dogs?

In dogs, fibrosarcoma tends to appear differently based on the location. When on the surface of the skin, they appear firm and raised. You might first notice it when you stroke and pet your dog. They can sometimes appear pink or reddish, depending on the location of the tumor. According to Dr.Malcolm Weir, DVM, these tumors may even ulcerate or bleed. On the other hand, fibrosarcomas that develop in the subcutaneous tissue may not be visible initially. These soft tissue tumors will feel more like a bulge. As for the location of these tumors, they can develop anywhere on your dog’s body. Typically, this includes the head and neck area and, sometimes, between toes as well. As with cats, your dog may not notice these tumors until they get so big that they rupture or damage surrounding tissue. Medication for the discomfort might then be recommended by your vet. 

What Breed of Dog Has Fibrosarcoma?

While fibrosarcoma can occur in any dog, there does seem to be a tendency for large and giant dog breeds to be more vulnerable. According to Dr. Melissa Boldan, DVM from the University of Missouri College of Veterinary Medicine, Doberman Pinschers, Golden Retrievers, and Irish Wolfhounds tend to see a higher number of cases of this type of cancer. While we aren’t exactly sure why this happens, a larger body size does equate to a greater number of cells. This increases the chance of genetic mutations and fibrosarcomas occurring. Large breeds also have shorter lifespans, and since cancer probability increases with age, we simply notice these dogs getting fibrosarcomas more often. Of course, small breed dogs that live eighteen to twenty years also have the same increased risk in their final years, but other illnesses and events may be more prominent for them. 

More on Cancer

Bone Cancer in Dogs and Cats
3 Ways to Save on Dog Chemo and Cancer Drugs
Nutrition for Dealing with Cancer in Dogs and Cats

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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