Fibrosarcoma Tumors


Fibrosarcomas are aggressive tumors that arise from the abnormal proliferation of cells known as fibroblasts. Fibroblasts are found in the connective tissues, including bone, skin, and their adjacent tissues.

While not exactly considered common in dogs, they represent the third most common type of canine bone tumor. In cats, however, fibrosarcoma tumors are more prevalent. In fact, fibrosarcoma has been deemed the most common tumor type of cats.

In dogs, fibrosarcomas tend to arise from the skin, the fat under the skin, and the tissues adjacent to these. These tumors are most often found in the trunk and extremities, the skull, and jaw.

Though highly aggressive, most canine fibrosarcomas are considered only locally invasive. Nonetheless, about ten percent of will metastasize (spread) to distant tissues.

As some breeds of dogs are overrepresented, a genetic origin for this disease has been inferred. The exact method of inheritance, however, is unknown.

In cats, three different forms of fibrosarcoma tumors are recognized:

  • The first is a version caused by the feline sarcoma virus (FSV) that tends to occur in young cats. This one affects many locations at once (multicentric).

  • The second is unrelated to the FSV and tends to occur in one location alone (solitary).

  • The third is by far the most common. This version has been associated with vaccination, particularly with vaccines that include aluminum (rabies and feline leukemia vaccines have been implicated more than others). This last form is referred to as a vaccine-associated sarcoma (VAS).

For cats, metastasis of fibrosarcoma tumors (usually to the lungs) happens in only 10 to 25 percent of cases. Except in the case of FSV-related fibrosarcoma and VAS, it’s impossible to pinpoint the exact cause of this cancer. Nonetheless, a combination of genetic and environmental factors is assumed.

Unfortunately, the prognosis for all fibrosarcoma patients is considered poor. Even with aggressive surgical and oncological intervention, over 70% of tumors recur within the first year. For VAS in cats, the rate jumps to more than 90%.

Symptoms and Identification

Fibrosarcoma tumors are typically firm but fleshy and adhere rigidly to their underlying tissues. They can appear as multiple nodules in the skin or as a solid swelling or plaque-like mass beneath the skin. The following tests are strongly recommended in course of initial diagnosis:

  • Physical examination

  • Complete blood count (CBC)

  • Blood biochemistry panel

  • Urinalysis

  • Chest X-rays

  • Fine-needle aspirate and cytological examination via microscopy

Fine-needle aspiration, though useful initially, offers insufficient information. The disease can only be diagnosed definitively by retrieving a specimen for the affected tissues (biopsy) and evaluating them through histopathology (microscopic analysis of the tissues by a board-certified pathologist). This can be achieved by surgically removing the bulk of the mass or by using tools to retrieve only a small bit of tissue.

Because these tumors are known to be highly invasive, definitive surgery to remove the entire tumor is best achieved only after defining the tumors’ anatomic limits via CT scan. This not only informs the surgeon’s surgical plan, it indicates whether the tumor is amenable to surgical resection in the first place. Sadly, many are not.

Affected Breeds

Fibrosarcomas can affect any breed of dog or cat. In dogs, however, Gordon Setters, Irish WolfhoundsBrittany SpanielsGolden Retrievers, and Doberman Pinschers are believed to be predisposed.


The most commonly applied treatment for fibrosarcoma is wide and deep surgical excision. Though general practitioner veterinarians are well equipped to achieve a definitive diagnosis, board-certified surgeons are strongly recommended for definitive mass removal. This is because surgical skill is highly correlated with longevity in fibrosarcoma cases. Moreover, the equipment employed by board-certified surgeons to help define the tumor's anatomical limits is rarely available to non-specialists.

Once surgery is complete, or in cases where surgery is either not possible or not elected, chemotherapy and/or radiation may be utilized to help keep tumors from recurring as quickly as they might otherwise.

It’s strongly recommended that owners who hope to gain the longest comfortable tumor-free time with their pets consult a board-certified oncologist.

Veterinary Cost

As with many cancers that require extensive and specialized surgery for treatment along with chemotherapy and/or radiation for best effects, the cost of this disease can be impressive and often prohibitive. Pets who suffer from fibrosarcoma tumors may even experience treatment costs that extend well beyond the $10,000 mark.

The cost of initial diagnosis is typically less than $500. Further diagnostics to help define the extent of the tumor and its reveal anatomic limits can top $2,000. The cost of surgery itself will depend on the surgeon’s degree of specialization along with the size and anatomical location of the tumor(s) but $1,000 to $3,000 is most typical. Chemotherapy will typically add another $1,000 to $5,000 (depending on the protocol elected and the patient’s size) and radiation may range from $5,000 to $10,000.

It cannot be overstated that the cost of diagnosis and treatment depends on many factors including geographic location (cost of living), standard of care (lower vs. higher standards of veterinary care), whether specialty hospitals are employed (higher quality equipment, certified personnel, and board-certification for veterinarians specialized in the fields of surgery and oncology).

Unfortunately, many owners elect not to treat their pets due to the extreme expenses associated with this disease.


There is no known method for the prevention of fibrosarcoma tumors in the dog.

In cats, the vaccine-associated form is one hundred percent preventable should owners decline to vaccinate them. However, declining the vaccine is neither wise nor recommended, especially since new vaccine technology appears to be responsible for a precipitous decline in VAS among felines.

Nonetheless, current guidelines for vaccination urge veterinarians to vaccinate cats below the knee. In this location, the tumor is much more amenable to surgical intervention than in the traditional location between the shoulder blades.


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