Oral Tumors

Tumors of the oral cavity are relatively common in both dogs and cats, representing approximately 6% of tumors in dogs and 3% of tumors in cats. They can be benign or malignant, and multiple histologic types have been described. The most commonly reported oral tumor in dogs is malignant melanoma, followed by squamous cell carcinoma (SCC), fibrosarcoma, and peripheral odontogenic fibroma. Many other tumor types have been reported and include chondrosarcoma, osteosarcoma, lymphoma, mast cell tumor, and plasmacytoma. In cats the most commonly reported tumors are SCC, fibrosarcoma, and osteosarcoma. Other types include odontogenic tumor, lymphoma, chondrosarcoma, salivary gland tumor, and melanoma.

Presenting Signs

Although oral masses may be found by owners or discovered incidentally on an oral examination by a veterinarian as part of a routine physical examination or during a dental procedure, animals often are clinically affected. The most common clinical signs in dogs and cats with oral neoplasia are halitosis, dysphagia, ptyalism, facial deformity, pain on opening of the mouth, weight loss, and epistaxis. In cats, owners also may notice decreased grooming or unkempt hair coat.

Diagnosis

Biopsy is an essential part of the evaluation of a dog or cat with an oral mass. It is not possible to distinguish tumor type or degree of malignancy based on visual inspection. Aspiration cannot often be performed without anesthesia or heavy sedation and is less likely to give a definitive diagnosis, which limits the usefulness of this test. Incisional biopsy and histopathologic evaluation provides important information regarding additional staging needed, treatment approach, and prognosis. The biopsy procedure should be planned properly so that the biopsy tract can be included easily as part of the excision of the tumor at the time of curative-intent surgery or included in the field of radiation if radiation therapy (RT) is performed. For tumors that appear locally invasive on physical examination, ideally the biopsy should be performed following imaging (see section on staging). If a definitive surgical excision is attempted, margin assessment is important to check for completeness of excision and the need for adjuvant therapy (see later).

Staging of oral tumors in both dogs and cats evaluates for the extent and invasion of the local tumor as well as the presence of regional or distant metastasis. A clinical staging system has been described by the World Health Organization for use with oral tumors (Table 81-1). This staging system can be used to guide pretreatment assessment and also is important for treatment planning. Documenting the exact location and size of an oral mass helps assess the local extent of a tumor, although radiographs and computed tomography (CT) can provide more complete information as to extent and bony involvement. To assess local lymph node involvement, palpation and cytologic evaluation of mandibular lymph node aspirates is an essential first step. Because lymph node drainage is variable in the head, contrast CT studies and ultrasonography can be performed to further assess local and regional lymph nodes, which include the mandibular, parotid, retropharyngeal, and cervical lymph nodes. Ultrasonographic guidance may be necessary for sampling of all but the mandibular lymph nodes. For malignant tumors, either three-view thoracic radiography or CT of the thorax should be performed to assess for pulmonary metastasis.

TABLE 81-1

World Health Organization Staging System for Oral Tumors in Dogs and Cats