Diagnosis of Fibrosarcoma in Dogs

Lili Duda, VMD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
We were notified today that our 7 year old Boston Terrier, has a well differentiated fibrosarcoma located in his back right leg near his knee. We were told that there is moderate to high potential for local recurrence and progression. There is low potential for regional and systemic metastasis.

We were told by our vet that this type of cancer is common among cats. However, she has never seen this type of cancer in dogs before.

When our vet did the biopsy to remove the mass, she indicated that she did not think that it was cancerous. Therefore, she was not careful about getting all of the tissue around the mass. The pathology test proved that it was fibrosarcoma. Our vet has suggested that our dog have surgery in three weeks (due to her opinion that additional anesthesia this soon after his first surgery for biopsy purposes would be too risky) to make sure that all of the tissue that was around the mass is removed And told us that our dog will probably have to have his leg amputated. While we respect our vet's opinions, we are concerned as to whether

    she is waiting too long to go back in to remove the remaining cancerous tissue and
  1. whether she is being too pessimistic in that we have read that a "well differentiated" fibrosarcoma has a decent chance of being cured during the initial surgery by removing the surrounding and underlying tissue. I would sincerely appreciate your opinion on this type of cancer with regard to dogs.

    Also — We would like to take our dog to a specialist who is familiar with this type of cancer for treatment. I would appreciate any guidance or referrals you could give me in finding a specialist in my area. As you might imagine, seeing as though he is nothing less than the heart of our family, state lines are not obstacles. While we prefer to stay in this region of the country, we are willing to consider almost anything in our attempts to save our dog's leg and perhaps his life.  
    Thank you very much for your time.

    Lili Duda, VMD, Editor of the OncoLink Veterinary Oncology Section, responds:

    Fibrosarcomas are a common skin tumor of both dogs and cats. Low grade fibrosarcomas (an indicated by the biopsy report) are generally locally very invasive, but unlikely to metastasize. Complete surgical excision can be curative; however, wide surgical margins are needed. The initial surgery (following the biopsy diagnosis) is the best chance for a cure, and it is always a good idea to seek the second opinion of a board-certified surgeon if there is any question about the surgery. This being said, it can be very difficult to obtain adequate surgical margins on a limb because of the lack of skin and soft tissue and proximity of vital structures (nerves, tendons, vessels). Amputation offers the best chance for a cure because the tumor is then removed with wide margins. A second option is to combine surgery with radiation therapy.

    There is a good chance that there is a radiation therapy facility within driving distance. Check your phone directory for a large teaching veterinary hospital. Surgery combined with radiation offer a fair to good prognosis of tumor control and is the next best option after amputation.

    In an otherwise healthy dog, and a well-equipped hospital with good monitoring equipment, a second anesthetic procedure should be no problem even within 24 hours. If the dog had any problems with anesthesia additional procedures would be a concern, but waiting a few weeks won't necessarily make any difference.

From the National Cancer Institute