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Fibrosarcoma Tumors in Dogs

Reviewed by Peter Kintzer DVM, DACVIM on Monday, April 7, 2014
Posted January 10, 2012 in Dog Diseases & Conditions A-Z


Fibrosarcomas are slow-growing, malignant (cancerous) tumors most often found in the connective tissue of the skin and beneath the skin. While these tumors may be removed successfully, they frequently recur after surgery. It is rare that fibrosarcomas metastasize (spread) to other parts of the body.

These tumors are difficult to classify and are often thought of as a group because of the parallel resemblance in their presentation. Therefore, there are several different names in addition to fibrosarcoma that you may hear when this category of tumors is discussed. Neurofibromas, peripheral nerve sheath tumors, spindle cell tumors, schwannomas, and hemangiopericytomas are all names for fibrosarcoma-type tumors.

Cause and Presentation of Fibrosarcoma Tumors
The cause of these tumors is unknown but it is thought that cancer, in general, is the result of many contributing factors that cause genetic injury to cells. Examples of such factors are exposure to chemicals or radiation (carcinogens), infection, hormonal changes, and, more often seen in cats, certain vaccinations. With cancer, the injured or mutated cells begin to multiply at an accelerated rate. The overgrowth of cells is what results in a tumor.

Fibrosarcomas are seen most often in large-breed, middle-aged to older male dogs. The tumors are often seen on the limbs but may be found on the trunk, as well. There have been incidences of an aggressive form of fibrosarcoma in dogs under 1 year of age, and in these cases, the prognosis is usually poor.

As these tumors are difficult to classify and are often thought of as a group, it is difficult to determine an accurate percentage of fibrosarcomas among diagnosed tumors. 

To ensure an accurate diagnosis, microscopic examination of the cells of the tumor is required.

There are different methods of sample collection that can be used to acquire these cells:

  • Fine-needle aspiration (FNA): Using a syringe and needle, the veterinarian will penetrate the tumor and withdraw cells from within the tumor. Generally no sedation is required for this procedure. FNA is not typically used to diagnose fibrosarcomas because, due to the nature of the tumor, it is difficult to aspirate the cells needed for identification.
  • Punch biopsy: Using either a scalpel or an actual punch (a circular-shaped knife that works in a “cookie-cutter” manner), the veterinarian can obtain, with minimal bleeding, a small biopsy that will include skin and underlying tissue for examination. This procedure sometimes requires light-to-moderate sedation. 
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