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Fibrosarcomas in Dogs

What Is a Fibrosarcoma in a Dog?

A fibrosarcoma in a dog is a form of cancer that originates in the connective tissue within the body. Connective tissue is present throughout the body, providing support and structure to muscles, ligaments, tendons, cartilage, nerves, bones, vessels, and fat. Fibrosarcoma tumors commonly develop in the connective tissue beneath the skin but can also arise in the nose, mouth, and bones. In cases where fibrosarcomas occur in the limbs or mouth, they may infiltrate the underlying bone, potentially leading to fractures.

Fibrosarcomas belong to the category of soft tissue sarcomas. While they typically grow slowly, they can exhibit local aggressiveness by invading surrounding tissues. About 10% of fibrosarcomas have the potential to metastasize, meaning they may spread to other parts of the body such as the lymph nodes and lungs. Fibrosarcomas are frequently diagnosed in dogs, with larger breeds showing a higher incidence of this cancer. Certain breeds like Irish Wolfhounds, Gordon Setters, Golden Retrievers, Brittany Spaniels, and Doberman Pinschers may have a genetic predisposition to developing fibrosarcomas.


The symptoms of fibrosarcomas in dogs vary depending on where they are located. Skin fibrosarcomas typically present as a solid lump on the body’s trunk, while tumors in the mouth, nose, or bones may cause drainage and discomfort in those specific areas. Dogs affected by fibrosarcomas often display one or more of the following symptoms:

  • Firm lump on the skin, sometimes ulcerated and bloody
  • Pain
  • Lameness
  • Nasal drainage
  • Difficulty opening the mouth
  • Decreased appetite
  • Halitosis (bad breath)
  • Facial deformity


The causes of fibrosarcomas in dogs, much like many other cancers, remain poorly understood. Cancer is generally believed to arise from a combination of genetic and environmental factors. Chronic stimulation from implants, such as bone plates from prior surgeries, or foreign objects can contribute to the development of cancer. Certain carcinogens, like exposure to radiation, are known to heighten the risk of cancer. Genetics and hereditary factors also play a significant role. In dogs, fibrosarcomas are more common in large breeds and tend to be diagnosed more frequently in older dogs, typically around the age of 10 years.

Cancer entails the uncontrolled division of cells. Ordinarily, cell division occurs under the body’s regulation for specific purposes. However, in cases of cancer in dogs, cells divide autonomously, disregarding normal regulatory mechanisms. Older animals are more prone to erroneous cell division, potentially harboring a greater number of mutated cells or experiencing a decline in the efficiency of eliminating problematic cells.


If your dog develops a new lump, it’s crucial to have it evaluated by a veterinarian promptly. It’s not feasible to ascertain whether a mass is cancerous solely by visual inspection. The most reliable method to identify the exact nature of a lump is to examine its cells under a microscope.

The two primary tests used to determine the nature of a lump are cytology and histopathology (biopsy). In cytology, your veterinarian will conduct a fine needle aspirate (FNA). During this procedure, a needle is inserted into the lump to collect cells, which are then spread onto a slide and examined under a microscope.

Grading of Fibrosarcomas in Dogs

In addition to identifying the type of cell present in a lump, examination also yields a grade for fibrosarcoma. Tumors are typically graded and staged, with grading indicating the “what” and staging indicating the “where.” Grading entails determining the type of tumor and its anticipated behavior.

Fibrosarcomas can be classified as Grade 1, 2, or 3, with Grade 1 tumors being the least aggressive and Grade 3 tumors being the most aggressive. More aggressive tumors necessitate more intensive treatment. Once a fibrosarcoma is diagnosed and graded, additional tests are recommended for staging. Staging involves evaluating the extent of the tumor’s advancement and identifying the locations where the cancer has spread. Your veterinarian may suggest blood work, X-rays, an abdominal ultrasound, and potentially a CT scan to search for evidence of cancer spread. The lungs and lymph nodes are the most common sites of metastasis for fibrosarcomas.


The primary treatment for fibrosarcomas in dogs typically involves surgery. Aggressive surgical intervention is often necessary to ensure complete removal of the cancer, although complete removal may not always be achievable. For instance, a fibrosarcoma on a limb may necessitate the amputation of the entire leg to eliminate all cancer cells. In situations where the tumor is located in the nose, mouth, or body wall, complete removal of the tumor may be challenging or unfeasible.

Following surgery, the excised mass undergoes histopathology to assess not only the grade but also the margins. The term “margins” refers to whether the surgery successfully removed all of the cancer. Ideally, surrounding normal tissue is excised to ensure that no cancer cells have infiltrated the surrounding tissue, reducing the risk of cancer recurrence.

In some cases where surgery is not viable, such as when the tumor is excessively large and closing the skin post-removal is impossible, radiation therapy may be recommended. Radiation can also be administered prior to surgery to shrink the tumor size. The age of the dog and any underlying health conditions are also factors influencing whether surgery may not be recommended.

Furthermore, oral medications may be prescribed to alleviate pain, reduce swelling, or treat secondary infections, especially if the mass is ulcerated. While fibrosarcomas generally have a limited response to chemotherapy drugs, pain medications may be recommended as an alternative when surgery isn’t feasible. Common medications include:

  • Carodyl 100
  • Gabapin
  • Domadol

Living and Management

Following surgery, it’s essential to limit your dog’s activity level to prevent undue stress on the incision. Typically, the post-operative recovery period lasts for about two weeks. A recovery cone will likely be provided to prevent your dog from licking or chewing the incision or irritating the surgical site. Ensure the incision remains clean and dry, and inform your veterinarian if there is any unusual drainage or if your dog displays lethargy or a lack of appetite.

When surgery isn’t feasible, the management approach focuses on ensuring your dog’s comfort. This may involve administering pain medications or antibiotics if secondary infections occur. Probiotics may also prove beneficial in maintaining balanced intestinal flora in dogs receiving pain medications or antibiotics, whether during the post-operative period or for supportive care.

The prognosis for fibrosarcoma can vary significantly, depending on factors such as the tumor’s location, its aggressiveness, and the extent of spread at the time of diagnosis. While fibrosarcomas tend to invade nearby tissue, they are less likely to metastasize compared to many other malignant cancers. This characteristic can result in longer survival times and a more favorable prognosis with appropriate treatment.

Fibrosarcomas in Dogs FAQs

How long can a dog survive with fibrosarcoma?

Survival times vary based on the fibrosarcoma’s location, its aggressiveness, and its spread at diagnosis. Dogs with lower-grade tumors that are completely excised may live for two to four more years, while those with higher-grade tumors and incomplete excision may survive less than a year.

Is fibrosarcoma treatable in dogs?

Fibrosarcomas can be treatable in dogs, especially in cases where they are low-grade and completely removed. While complete cure is less common, it remains a possibility.

How quickly do sarcomas grow in dogs?

Fibrosarcomas in dogs typically grow slowly. Nonetheless, they are highly invasive and have a tendency to infiltrate surrounding tissues.

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