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Oral and perianal tumors (Proceedings)

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Nov 01, 2010

Canine
Oral tumors account for ~6% of canine tumors making them the fourth most common neoplasm in that species. Four major histologic classifications; fibrosarcoma, melanosarcoma, squamous cell carcinoma and the epulides account for the vast majority of cases. Other less common diagnoses include lingual tumors, tonsillar SCC, viral papillomatosis, eosinophilic granuloma complex and papillary squamous cell carcinoma of young dogs. Because the treatment options and prognosis for each tumor are often unique, a definitive diagnosis is imperative.

Fibrosarcomas
This tends to be a disease of large breed, middle age dogs. Males are slightly overrepresented and these tumors often affect the palate. They are slow to metastasize, but notoriously difficult to control locally. Wide surgical excision is the treatment of choice and presurgical imaging with a CT scan or MRI is indicated in almost all cases. Adjuvant radiation therapy is effective on microscopic disease, but works poorly in the face of a large tumor burden.

One variant to watch for is the histologically low-grade, biologically high grade fibrosarcoma. On biopsy samples these will come back as granulation tissue, but visibly invade into bone and will metastasize to regional lymph nodes. If there is any doubt about the original histopathology, give a more thorough history and ask for a review or rebiopsy the lesion.

Epuli
By definition these are benign tumors and may be described as fibrous, ossifying or acanthomatous (currently called ameloblastoma). The most aggressive is the ameloblastoma which is highly invasive and always has bony involvement. They often occur in the rostral mandible or near a carnassial tooth in middle age to older dogs. Both surgical resection and/or radiation therapy should be very effective in attaining long term control.

Squamous cell carcinomas
iagnosis is usually straightforward and can involve any location in the oral cavity. As a general rule, the more rostral the tumor, the more benign it's clinical course. Those in the tonsil will metastasize in the majority of cases. As with fibrosarcomas, surgery remains the mainstay of curative therapy. They are more radiosensitive than most fibrosarcomas and radiation therapy is often added to their treatment plan. Advanced imaging will be important to plan the surgical resection and/or the radiation therapy. Evidence is now accumulating to indicate that toceranib (Palladia), a tyrosine kinase inhibitor with anti-angiogenic activity, may also have some activity. It is unlikely that as a single agent the toceranib response rates will be high, but its addition to surgery or radiation therapy may make a difference. It will require many years of accumulated data before definitive recommendations can be made.