Oral Tumors in Dogs - Fibrosarcomas

By Tammy Hunter, DVM; Jan Bellows, DVM, Dipl. AVDC, ABVP; Christopher Pinard, DVM

What is an oral fibrosarcoma?

Fibrosarcomas arise from the fibrous tissues of the oral cavity and are the third most common oral tumor in dogs. They commonly invade the adjacent tissues but only about one third will spread to other organs.

What causes this cancer?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.

Fibrosarcomas are typically seen in medium to large breed, middle aged dogs. The Doberman pinshcer and Golden Retriever are most commonly affected.

What are the signs that my dog has this type of tumor?

Lesions are firm and smooth and may appear as swollen areas arising from any location within the mouth. They frequently ulcerate (break open) and bleed and may also become infected. These tumors may look small but may extend deeper into the tissues than expected, invading the underlying bone.

The signs your dog may exhibit depend on the location, size, how much the tumor has spread. Swelling inside and outside of the mouth as well as oral pain is usually apparent, especially in dogs with tumors that have invaded the underlying bone. Your dog may exhibit signs such as bad breath (halitosis), excessive drooling, panting, discomfort while eating or dropping of food, lack of appetite, reluctance to be touched on the head, and facial swelling.

How is this cancer diagnosed?

Fine needle aspiration (FNA) may be performed, but usually cannot accurately diagnose these types of tumors. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

For a definitive diagnosis, and prediction of how the tumor may behave (grow or spread), a biopsy is required. A biopsy is a surgical excision of a piece of the tumor. Your veterinarian may remove a small piece of the tumor, or the entire tumor for diagnosis. Pieces of the tumor are then examined under the microscope by a pathologist. This is called histopathology.

How does this cancer typically progress?

These tumors tend to behave aggressively by invading the local and surrounding tissues, with a lower tendency to metastasize (spread to other organs). About 24% of cases will metastasize. Some fibrosarcomas will look non-aggressive (low grade) when observed under the microscope; however, they will behave aggressively. Intense therapy with any diagnosis of a fibrosarcoma, regardless of suggested behavior, is recommended.

Full staging (searching for potential spread to other locations in the body) is highly recommended for malignant tumors, as they tend to spread. This may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound. If lymph nodes, particularly those located under the chin (mandibular lymph nodes), are enlarged or feel abnormal, further sampling by FNA may be pursued to determine if spread is present.

What are the treatments for this type of tumor?

Surgical removal is the standard method for treating fibrosarcomas. A CT scan or MRI of the head and/or neck region are generally recommended before surgery to determine the extent of disease and for surgical planning. If lymph nodes under the chin (mandibular lymph nodes) are affected, they typically will be removed during surgery.

Depending how invasive the tumor is, surgery may involve removing a portion of the top or lower portion of your dog’s jaw. Although this type of surgery sounds daunting for you and your dog, many of these tumors are painful and surgical removal provides relief. Most dogs respond well to this type of surgery.

Is there anything else I should know?

Even with surgery, recurrence (or regrowth) is possible. These tumors do not respond well to chemotherapy or radiation therapy alone; however, in conjunction with surgery, radiation therapy has been shown to provide the longest survival time.

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