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Resource Library: Oral Tumors, Canine

Oral tumors account for approximately 6% of all malignancies in dogs. The mouth and pharynx are affected 2.6 times more commonly in dogs than cats. The cause is unknown with the exception of canine papillomatosis that is caused by the papovavirus. These tumors can arise from the gingival, buccal mucosa, tongue, mandible, maxilla, dental structures and tonsils. Breeds that are most oftent affected are Cocker Spaniels, Poodles, German Shorthaired Pointers, Weimaraners, Golden Retrievers and Boxers.

The four most common tumors that affect the oral cavity in the dog include Squamous Cell Carcinoma, Fibrosarcoma, Melanoma and Epulides. A definitive diagnosis is made by tissue biopsy performed under general anesthesia. Further diagnostic tests such as regional lymph node aspirates and chest radiographs and/or treatment decisions are performed based on the specific tumor type determined on histopathology.

1. Squamous cell carcinoma usually occurs in older large breed dogs and often affects the rostral mandible (lower jaw). It can spread to the regional lymph nodes and lungs. The bone of the jaw cab be invaded by the tumor. The treatment of choice is complete surgical excision or radiation. Prognostic factors include; previous treatment, stage of disease, location (rostral :front of the mandible) is better than caudal: back of the mandible), grade (degree of malignancy), age (younger animal fare better) and the size of the treatment field if the tumor is radiated. Tongue squamous cell carcinomas, have a high rate of spread to the regional lymph nodes and lungs with a 50% survival at one year. Squamous cell carcinomas of the tonsils have a 10% survival at one year.

2. Fibrosarcoma affects middle-aged large breed dogs. It is more common in male dogs and often occurs on the palate. The regional lymph nodes are rarely affected and occasionally the lungs have metastasis. Bone involvement is common with these tumors. Surgical excision is the treatment of choice but local recurrence is common with large tumors. These tumors have a poor to fair response to radiation therapy. Prognostic factors are size of tumor and grade.

3. Melanoma occurs in older small breed dogs most commonly. The buccal mucosa is commonly the area affected. Regional lymph nodes and lungs are commonly affected with metastases. Two thirds of melanomas are black in color and will invade bone in some cases. These tumors are considered poorly responsive to traditional daily radiation protocols but may be better responsive to coarse fractionation (83%), although the response times are usually short term. Prognostic factors include size, presence of metastasis to the lymph nodes, ability to achieve clean margins, and location (mandibular tumors do better than other locations.

4. Dental tumors such as epulides (acanthomatous, fibromatous and ossifying) affect middle-aged female, large breed dogs most commonly. They often occur in the rostral mandible but rarely metastasize to the regional lymph nodes or lungs. They frequently invade bone. The prognosis is excellent and surgery is considered the treatment of choice.

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