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Fibrosarcoma is a type of tumor that arises out of bone and connective tissue in dogs and cats, but these tumors are far more common in dogs than in cats. In the canine, fibrosarcomas most commonly arise from the mouth from inside the jaw bone. In cats, fibrosarcomas arise most commonly from a point on the body where a vaccine has previosly been given., giving rise to the characterization: vaccine induced fibrosarcoma. The main associated vaccines in the development of feline vaccine induced fibrosarcoma are rabies and feline leukemia. However, the overall incidence of these types of tumors are considered to be quite rare. It is an overwhelmingly accepted notion that the risk of disease for unvaccinated cats far outweighs the danger of developing vaccine induced fibrosarcoma at a vaccine site.

Fibrosarcomas have a low incidence of metastasis (spread to other tissues). While they do not tend to metastasize, they are invasive tumors that root themselves deeply in underlying tissue, causing destruction of underlying tissue as they grow.

Treatment for fibrosarcoma is primarily surgical, with success dependent upon the ability of the surgeon to resect the entire tumor. This is largely dependent on how deeply rooted the tumor is, and what anatomical location the tumor arises from. Fibrosarcomas that arise from the mouth and nasal sinuses pose much greater challenge surgically resecting than those arising from the body. However, deeply rooted and/or large fibrosarcomas can be very difficult to completely surgically resect from any location on the body due to sensitive anatomical structures of inability to close such a large resultant defect. For this reason, surgery often has to be augmented with radiation and chemotherapy to offer the best possible prognosis.

Regarding prevention of specifically feline vaccine induced fibrosarcoma, the veterinary pharmaceutical Merial offers a line of both adjuvant free rabies and feline leukemia vaccines for prevention of vaccine induced tumors. It is the adjuvant component of the vaccine (the part of the vaccine that prolongs the time of protection of vaccines) that is believed to be responsible for mutations that lead to fibrosarcoma formation. Since the adjuvant imparts extended protection to a vaccine, adjuvant free vaccines only last one year so must be boostered yearly.

I am not certain of the overall impact these adjuvant free vaccines have had on the incidence of feline vaccine induced fibrosarcomas, but from personal experience, they have seemed to eliminated them altogether. In my first three years of practice, I saw about 1-2 cases of feline vaccine induced fibrosarcoma per year. Since adopting the Merial adjuvant free vaccines for cats in 2004, now 7 years later, I still have yet to see one case where I can verify that only these vaccines were used throughout a patient’s entire life. Time will tell, but my experience seems promising.

Since these vaccines also seem to cause a much lower rater of vaccine allergic reaction in cats, I think it is a good idea to use them anyway. They cost slightly more than conventional vaccines, but the modest additional amount cat owners pay from my view is clearly worth it.


Roger L. Welton, DVM
Founder and Chief Editor,
President, Maybeck Animal Hospital

Article updated 10/22/2012

13 thoughts on “Fibrosarcoma

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