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Treatment of Fibrosarcoma in Dogs

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Lili Duda, VMD
Last Modified: November 1, 2001

My dog was just given the results of her biopsy last week from a tumor on the lower jaw (under the bottom back molar) in the soft tissue-- it was fibrosarcoma- and the vet did remove it!

My questions are;

• Why does she need radiation?
• If the tumor is removed-- why can't we think that the cancer is gone?

KTT

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

Dear KTT,

Fibrosarcomas are one of the more common cancers in the oral cavity of the dog. They can be very invasive locally, but are unlikely to metastasize (that is, spread to other areas of the body like the lymph nodes and lungs). Every canine patient should have a complete staging evaluation prior to treatment for cancer. Staging refers to the process of determining how advanced a cancer is and if it has spread. We "stage" an animal through the use of tests such as x-rays, ultrasound, blood work, lymph nodes aspirates and bone marrow aspirates. This is helpful because it allows us to determine the best treatment options and to predict the outcome of treatment.

Complete surgical removal is the treatment of choice for fibrosarcomas, when possible. Both the size and location of the tumor determine this. Consultation with a board-certified surgeon is recommended. Surgery requires that all the tissue around the tumor be removed, including the bone and an area of normal-looking tissue around the tumor. This is because the tumor can extend far beyond the portion that can be seen with the naked eye (or even what can be seen on regular X-rays). The portion of the tumor that is visible is only the "tip of the iceberg", with the bulk of the tumor extending deep into the underlying and surrounding tissues. There is little to no benefit in removing only the superficial portion of a tumor, because the "roots" remain, and the tumor can regrow very quickly.

After the tumor and surrounding tissue is removed, it is sent to a veterinary pathologist. The pathologist examines the tissues under a microscope to see whether any tumor cells are present at the edges. If there is any question that the surgery did not remove the entire tumor, then radiation therapy can be used to try and destroy any remaining cancer cells.