This tumour type is located in the oral cavity.

Behaviour

Generally speaking, fibrosarcomas mostly invade the local tissue, but can also metastasize towards the lymph nodes, followed by the lungs in up to 30% of cases.

Prevalence

The oral fibrosarcoma is the third most frequent tumour in the oral cavity of the dog.

Breed predisposition

Fibrosarcomas appear mostly in large breeds, in particular the Golden and Labrador retriever with a median age of 7 to 8 years.

Symptoms

It manifests as a tissue mass that grows quickly, especially when located on the jaw (located more frequently on the front of the upper jaw than the lower jaw). Depending on where the tumour is situated, different symptoms will be visible. A tumour on the hard palate can disturb swallowing, a tumour on the gum can cause bleedings due to contact with teeth/other.

It isn’t always easy to see the difference between a proliferation of the gum and the formation of a tumour. Therefore, it is important to examine this!

Tissue biopsy

The information provided by a tumour biopsy can be deceitful: this tumour type can look benign, but act malignantly. This is common for fibrosarcomas of the hard palate and the upper jaw (between the canine and molars).

Following diagnostic steps are advised for oral tumours suspected of malignancy:

• Radiographic photos of the oral cavity and the thorax. In order to be able to take the radiographic photos of the oral cavity, the dog must be sedated. Damage to the bone only appears when already 40% of the bone is destroyed. It is therefore possible that the bone is damaged, but that this is not yet visible on a radiographic photo. This means that a normal radiographic photo does not exclude bone damage.
• Punction (cytology) of local lymph nodes. The size of the lymph node does not reflect the presence of metastases. The lymph nodes that are draining the tumour can be detected via lymphoscintigraphy or contrast ultrasound. This way, more specific punctions can be taken and their contents analyzed for the presence of metastases.
• Tissue biopsy.

Through this evaluation, it is possible to have an idea of the prognosis and the possible treatment options.

Imaging

A CT and/or MRI scan can give even more information on the tumour (this is particularly useful to have a more precise estimate of bone damage vs radiographic photos, and of the distribution of the tumour towards the nasal cavity, the throat and/or the eye socket).

The best survival is obtained with a combinatorial approach: e.g. surgery and radiotherapy or radiotherapy combined with hyperthermia.

Surgery

Surgery is the most common treatment for oral fibrosarcomas. Surgical resection of the tumour can cure the dog if there are no metastases present. Margins of at least 2 cm are necessary in case of fibrosarcomas.

The secondary effects depend on the quantity of tissue that needs to be removed. They can consist of wound dehiscence, nose bleeds, increased salivation, difficulties closing the mouth and picking up food with the mouth.

After elimination of (a piece of) the lower jaw, local relapse is reported to be 59% in dogs. On average, dogs survive during 11 months after surgery and 50% are still alive after 1 year.

After elimination of (a piece of) the upper jaw, local relapse is reported to be 40% in dogs and the average survival time is 12 months. When only surgery is performed, 50% of dogs is still alive after 1 year.

Cryosurgery is only advised for tumours less than 2 cm in diameter and attached to the bone or minimally invasive. For larger tumours, classic surgery is advised.

Radiotherapy

Radiotherapy can be used as sole treatment (with a curative or palliative purpose), or as supplementary treatment for incompletely resected tumours or tumours with a very aggressive local behaviour. In general, fibrosarcomas are considered to be tumours that are not very sensitive to radiotherapy and its use is advised in combination with other treatments.

The acute effects of radiotherapy are regularly seen and consist of local baldness, thinning of the skin accompanied by production of fluids, inflammation of oral mucous membranes, difficulties swallowing and changes to the eye (inflammation of the eyelid, the conjunctiva, the cornea or the internal eye). The degree in which these effects are seen depend on the intensity of the irradiation protocol and these symptoms are in general quickly resolved. Late complications are rare (less than 5% of cases), and consist of permanent local baldness, thickening of the skin, bone necrosis and formation of fistula between the nasal and oral cavity, development of a second tumour in the radiation field, desiccation of the eye/mouth, cataract, loss of function of the retina.

• When only radiotherapy is used as treatment, the mean survival time is 7 months.
• Radiotherapy can be combined with hyperthermia (a treatment during which a tumour is warmed up until 45°C which causes damage within the tumour, but minimal damage in the normal tissues). With this combination, 50% of dogs were still alive 1 year after treatment. However, these treatments have only been tested in a small number of dogs (max 17) and these results must be confirmed with a higher number of dogs.
• The best results have been seen with the combination surgery and radiotherapy: after these treatments, relapse has been reported to be limited to 32% of dogs and the mean survival time surpasses 2 years.

The combination of radiotherapy and surgery offers the best chances to locally control the tumour.

Hyperthermia

Hyperthermia on its own does not offer an advantage as opposed to cryosurgery and is mainly used as a supplementary treatment for radiotherapy.

Chemotherapy

There is insufficient proof that supplementary chemotherapy has an effect on the prevention of metastases.

The prognosis for fibrosarcomas in the oral cavity is reserved. These tumours are locally aggressive and their local control is more often an issue than the metastases. The metastases appear in the lymph nodes in 19-22% of dogs and in the lungs in up to 27% of dogs.

The bigger the tumour is, the worse the prognosis.