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Tumors of the mouth
Oropharyngeal Cancer

Oropharyngeal Cancer (Tumors of the Mouth)

Pamela A. Davol, 76 Mildred Avenue, Swansea, MA  02777-1620.
http://pdavol@labbies.com

Orophayngeal tumors account for about 6% of all tumors occurring in the dog. There are a number of different types of tumors that may develop in the oral cavity of the body. Among them, the most common is melanoma followed by fibrosarcoma, squamous cell carcinoma and adenocarcinoma. Melanoma involves tissues of the gums most frequently, followed by the tongue, lip and palate. Soft tissue tumors will sometimes invade the jawbones. This is particularly the case of osteosarcomas. Cocker Spaniels have an increased incidence for melanoma compared to other breeds, and there may be a slight predominance for this tumor-type to occur in males.

AVERAGE AGE OF ONSET
Cancerous lesions of the oral cavity may present at any age with the highest frequency occurring between the ages of 7-11 years.

CAUSE
A tumor virus, called papillomavirus, is suspected of playing a role in oncogene activation associated with the development of carcinomas and sarcomas of the oral cavity. Dogs with oral and ocular papillomas (benign tumors) reportedly are at increased risk to developing malignant tumors. Dogs living in the city are at higher risk to developing malignancies associated with the tonsils. One study found a significant increase of risk for sinonasal tumors in pet dogs in homes using indoor coal or kerosene heaters suggesting strong evidence for environmental carcinogens in the development of oropharyngeal cancers.

SYMPTOMS
Unfortunately, malignancies of the oral cavity are not often found until the disease is in an advanced stage. Increased salivation, difficulty chewing, loss of appetite, weight loss, difficulty swallowing, bad breath, and bloody saliva are all symptoms of oropharyngeal cancers. Tumors involving the tonsils or the base of the tongue may also cause difficulty breathing. Loose teeth in an otherwise healthy mouth may also signal the presence of bone lesions. Sarcomas may present as ulcerating mass lesions, however, carcinomas may be less obvious in terms of detection.

DIAGNOSIS
Dogs presenting with tumors of the oral cavity must undergo biopsy of the lesion for identification of tumor-type. Additionally, x-rays of the local and surrounding area of the tumor as well as films of the chest are usually required to determine extent of the spread of the disease. Many melanomas and some carcinomas will have already metastasized to the lungs by the time the dog is identified as having an oral tumor. Additionally, it is not uncommon for tumors of the soft tissues of the mouth to invade underlying bone. Regional lymph nodes should be examined for possible involvement, and suspicious nodes should be biopsied by fine-needle aspiration for evidence of malignant cells. Computed tomography (CT) may be valuable for determining the extent to which the nasal cavity may be involved.

TREATMENT
Surgery involving the removal of portions of the effected upper (maxillectomy) or lower (mandibulectomy) jaw results in average survival times of 8 or 11 months, respectively. The best outcomes are reported for radical excision in which an average of at least 2-cm of surrounding normal tissue is removed with the diseased tissue. In the cases of incomplete excision or inoperable tumors due to wide spread invasion, radiation therapy may provide palliative control of some radiation-responsive tumors. Radiation therapy may be combined with chemotherapy, however, no significant advantage of providing longer survival has been observed for this combination compared to radiation therapy alone. For chemotherapy alone, squamous cell carcinomas are moderately responsive to Cisplatin or Carboplatin, and sarcomas demonstrate a 30-50% response rate to Doxorubicin treatment.

PROGNOSIS
Early detection, when oropharyngeal tumors are less than 2 cm in diameter, provides a better outlook for therapeutic response and long-term prognosis since likelihood of metastasis increases with the size of the primary tumor.

Melanomas of the oral cavity are usually resistant to radiation therapy and carry a poor prognosis due to the high incidence of metastases associated with this tumor-type. Average survival following therapy for melanoma is about 8 months.

Fibrosarcomas present more problems associated with local invasion than with distant metastases. Additionally, this tumor-type appears to be extremely resistant to local control when it occurs in dogs under the age of 2 years. In general, however, fibrosarcomas are responsive to radiation therapy with control of tumors lasting an average of 12 months. Greater tumor control has been observed in dogs treated with a combination of radiation therapy and local hyperthermia (heat therapy). Most successful treatment regimens combine surgery with radiation therapy (before or after surgical excision) and chemotherapy.

Squamous cell carcinomas are locally invasive with preponderance toward invading underlying bones, however, metastases associated with this tumor-type are rare in the dog. Average survival of dogs treated with surgery and radiation therapy is a little over 1 year. An exception to this occurs when this tumor-type develops in the tonsils. Average survival decreases dramatically (to about 4 months) even with surgery and radiation therapy, and is associated with the increased tendency of the tumor to metastasize from this location. Addition of Cisplatin or Doxorubicin to the standard treatment regimen may assist to prolong survival.

Osteosarcomas of the oral cavity bear a particularly dismal prognosis due to both local invasiveness and high incidence of metastases. Average survival of dogs undergoing treatment with surgery and radiation is about 4-5 months. Addition of chemotherapy to the treatment regimen may further increase anticipated survival of dogs with this tumor-type

PREVENTION
The increased incidence for dogs with papillomas to develop oropharyngeal tumors combined with the decreased incidence of these tumors in dogs immunized against papillomavirus provides strong evidence that predisposition to oral cavity tumors is virally induced. Additionally, it has been found that dogs who are immunosuppressed due to therapy with glucocorticoids show increased risk to infection with the papillomavirus. Therefore, factors such as viral infection and immunosuppression combined with environmental carcinogens may be the most common events leading to development of oropharyngeal tumors.

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OROPHARYNGEAL CANCER

(Mouth cancer and cancer of the pharynx)

This information is provided by Provet for educational purposes only.
You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Note for Pet Owners:
If your pet develops a swelling or growth in it's mouth seek the advice of your veterinary surgeon.

Topics on this Page:
Description
Dogs
Cats
Signs
Diagnosis
Treatment

Description
Cancers which occur in the mouth or in the region of the pharynx (at the back of the mouth) can be either malignant or benign. Some forms of malignant cancer in this region (e.g. melanoma) are extremely serious, spread rapidly and can be life threatening. Others are not serious at all, although they can cause alarm to an owner (e.g. oral papillomatosis - warts). As with all tumours early accurate diagnosis is important so that appropriate treatment can be started as soon as possible.

Dogs
The most common malignant cancers to occur in the mouth or pharynx of the dog are melanomas, squamous cell carcinomas and fibrosarcomas. The first two can be very serious and malignant melanomas in particular can spread (called metastatic spread or metastasis) very rapidly to other organs such as regional lymph nodes and the lungs. Melanomas are more common in the Chow-Chow and Great Dane and unfortunately carry a poor prognosis.

Fibrosarcomas are seen in younger dogs and rarely spread but they frequently recur locally after treatment.

Epulides are benign and, although they can grow to be quite large, present problems with eating, and sometimes ulcerate and bleed they are not life threatening. Epulides are cauliflower-type fibrous growths which occur along the gum margin (hence they are called "gingival cancer", and they are sometimes called periodontal fibrous hyperplasia). They are common in brachycephalic (short-nosed) breeds of dog, especially the Boxer and English Bulldog.

In general cancers occur more frequently with advancing age.

Young dogs, however, frequently develop warts in the mouth and on the tongue and these are cause by papilloma virus and the warts themselves are benign.. The warts can affect eating and sometimes localised secondary infection can occur giving a foul smell on the breath, but the disease is not serious and is self-limiting, lasting only about 6-12 weeks.

Cats
In cats about 50% of cancers in the mouth involve the tongue, and the most common oropharyngeal cancer is squamous cell carcinoma.

Signs
The signs associated with oropharyngeal cancers will vary depending upon the site of the tumour and the type of cancer.

Typical signs are :

Difficulty or pain when eating or swallowing
Bad breath (halitosis)
Bleeding from the gums or tumour mass
Ulcers in the mouth
Development of abnormal growths in the oral cavity or pharynx - including the tonsilar crypt.

Diagnosis
Sometimes diagnosis can be made based upon the typical appearance of the cancer, the history and presenting signs. A black pigmented, ulcerated bleeding tumour that has appeared and grown very quickly in the mouth of an ageing Chow-Chow is likely to be a malignant melanoma, whereas multiple small cauliflower-type growth in the mouth of a young puppy are most likely papillomas.

In other cases the type of tumour-type will not be obvious and accurate diagnosis will rely on histological examination of a biopsy, or removed tumour.

In all cases it is important to examine local lymph nodes in the throat or neck to detect evidence of spread. Enlargement or pain can be detected by feeling the site, but an Xray of the neck may be needed to identify retropharyngeal spread. An enlarged retropharyngeal lymph node is seen as a large soft tissue mass under the cervical spine, often displacing the windpipe (trachea) and gullet (oesophagus).

A chest Xray is very important to ensure that spread to the lungs has not occurred.

Any evidence of spread is a poor prognostic indicator which may affect the method(s) of treatment used. Ensuring a satisfactory quality of life is often more important than prolonging life in patients with advanced metastatic disease.

Treatment
There are a wide range of treatment possibilities from surgical excision for benign, well localised cancers, to chemotherapy, radiotherapy and hyperthermia for malignant cancers.

Excision is recommended for benign cancers - e.g. warts, and epulides - though the latter frequently recur.

Radiotherapy is recommended for oral squamous cell carcinomas and the prognosis is good.

Squamous cell carcinoma of the tonsil in older dogs however, is a much more serious form of cancer because it often spreads to the retopharyngeal lymph nodes and frequently spreads further to the lungs.

Combination therapies are usually advocated for the malignant tumours.
   
Copyright (c) 1999 - 2007 Provet. All rights reserved. mailto:info@provet.co.uk
reprinted with kind permission from Mike Davies

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The above information is simply informational. It's intent is not to replace the advice of a veterinarian nor to assist you in making a diagnosis of your pet. Please consult with your own veterinarian for confirmation of any diagnosis. Your pets life may depend on it.