Introduction

Treatment of orofacial tumours requires careful planning to preserve sensitive as well as critical organs within this area. In order to carry out successful treatment the veterinarian requires knowledge of anatomy, tumour biology and the treatment options.

The owner's wishes, pet's overall health, probability of cure, availability of treatment, and cosmetic effect and function all need to be considered when deciding on the management of a patient.

Staging (TNM)

Once the above factors have been taken into consideration, staging is the most important process of decision-making. Staging a tumour involves assessing the tumour (type, size, location and grade), the local lymph nodes and the rest of the body for distant metastases.

Tumour

The type of tumour will provide information regarding the likelihood of spread and the probability of a cure. The latter is further influenced by the location, size, invasion of surrounding tissue and grade of the tumour. As many of these tumours are ulcerated and have secondary bacterial infections, a large deep biopsy sample should be taken to ensure a representative specimen is obtained. Establishing a definitive diagnosis is essential to planning the most appropriate treatment.

Figure 1. Common oral tumours in the dog and cat.

Location

As there are vital and sensitive organs in this region, location plays a major role in deciding on appropriate treatment. More rostral tumours and those on the face are usually identified earlier than more caudal tumours. As such they are usually smaller on presentation. Rostral tumours are also more amenable to treatment--located further away from vital organs, allowing a surgical approach with a partial or complete maxillectomy or mandibulectomy. This area also has less serious side effects from radiotherapy. More caudal tumours cannot be excised as easily and margins are harder to obtain. Radiotherapy can cause more damage in this area and is limited by the proximity of the brain, eyes, frenulum and pharynx.

Size and Invasion

Smaller tumours have the greatest chance of complete removal with adequate margins, and therefore cure. Primary tumours will often require additional diagnostic imaging to assess the degree of invasion of surrounding tissue. This may involve radiography or more advanced imaging such as MRI or CT.

Clinical staging system for oral tumours:

 Tis: Tumour in situ

 T1: Tumour <2 cm in diameter at greatest dimension

 T2: Tumour 2-4 cm in diameter at greatest dimension

 T3: Tumour >4 cm in diameter at greatest dimension

 a = without evidence of bone invasion

 b = with evidence of bone invasion

Grade

Higher-grade tumours tend to have a worse prognosis, while lower-grade tumours tend to have a better prognosis. An exception to this is apparent "low-grade" oral fibrosarcomas, which have an aggressive behaviour.

Node

The regional lymph nodes are assessed by palpation to determine their size, shape, consistency and fixation to adjacent tissues. The ipsilateral submandibular lymph node should be aspirated. The retropharyngeal and parotid lymph nodes also drain the oral cavity and may need to be assessed with imaging if the tumour is malignant. Invasion of the lymph nodes will influence treatment and help to establish prognosis. The lymph nodes can be removed surgically or irradiated. The prophylactic removal of lymph nodes is controversial. Lymph node involvement may worsen prognosis and as such influence whether the patient is treated with curative or palliative intent.

Metastasis

The patient should be screened for distant metastases. This will usually involve radiographs of the thorax. Whether other body organs are screened is determined by the predicted behaviour of the specific tumour type. Prognosis is generally poor if there is evidence of distant metastasis. Although chemotherapy would generally be the treatment of choice for distant metastasis, orofacial tumours tend to respond poorly to this mode of treatment. Therefore, the goal of treatment is to improve the quality of life of the patient. This usually involves reducing/resolving oral discomfort, which is the major reason for morbidity in this group of patients. This can potentially be addressed with surgery, radiotherapy or analgesics.

Common Canine Orofacial Tumours

Malignant melanoma: Melanomas in this location are highly malignant. Tumours <2 cm, with no evidence of lymph node involvement, have a better prognosis. There is no effective treatment for metastases but there is ongoing research into immunotherapy. Treatment tends to be palliative with surgery or radiotherapy.

Squamous cell carcinoma: Prognosis is correlated with tumour location. Lingual and tonsillar squamous cell carcinomas metastasise to local lymph nodes and are associated with a poor prognosis. Rostral squamous cell carcinomas can be cured if surgical margins can be obtained. They are very invasive and often require more advanced imaging to appropriately plan treatment. Canine gingival squamous cell carcinomas are moderately radiosensitive.

Fibrosarcoma: This type of tumour has an aggressive local behaviour, often invading bone and adjacent structures. It is difficult to achieve local tumour control with surgery and adjunctive radiotherapy should be considered to improve prognosis.

'Epulides': These are benign tumours, which can be cured with surgery. They are also radiosensitive.

Osteosarcoma: Osteosarcomas of the mandible have lower rates of metastasis than their appendicular counterparts. They should therefore be treated surgically.

Mast cell tumour: Cutaneous mast cell tumours in this location should be treated as for the rest of the body. The challenge is obtaining deep margins. Therefore surgery and adjunctive treatments need to be considered.

Common Feline Orofacial

Tumour squamous cell carcinoma: The behaviour of these tumours is dependent on their location. Oral squamous cell carcinomas are painful and by the time the patient is brought to the surgery, treatment is limited and the prognosis is poor. Tumours on the pinna, nasal planum and eyelids rarely metastasise and have a slow progression. The depth of the tumour determines the best treatment option. Superficial tumours can be treated with photodynamic therapy, radiation or surgery. Deeper tumours need to be treated with surgery.

Summary

In order to plan the most appropriate treatment for orofacial tumours, the veterinarian needs to have a full understanding of tumour behaviour. The type and extent of the primary tumour needs to be established and the patient assessed for regional lymph node involvement and distant metastases.

References

1.  Dobson JM. TNM Classification and clinical staging. In: Dobson, JM; Lascelles BD. BSAVA Manual of Canine and Feline Oncology (second edition). Gloucester, BSAVA, 2003; 18-20.

2.  Liptak ML, Withrow SJ. Cancer of the gastrointestinal tract. In: Withrow and MacEwens's Small Animal Clinical Oncology. Canada, Saunders Elsevier, 2001; 455-477.