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.
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.
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.
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.
Keep in mind that approximately 1/3 of these tumors will be amelanotic and may require special stains. They are generally found in the older, smaller pet and males are overrepresented. Early metastasis is typical and every case should have lymph node aspirates and thoracic radiographs performed. Two very important prognostic variables are the size of the original tumor, and the ability to control it the first time, i.e. recurrence is invariably associated with metastatic disease. Again a carefully planned surgery is the treatment of choice and small tumors (<2 cm) that are completely excised have a relatively good prognosis with median survival times of 511 days. Larger tumors and those that have metastasized require multimodality therapy and have a much more guarded prognosis. Still, the addition of a melanoma treatment vaccine can increase disease free intervals significantly and is effective in ~55% of cases. Coarsely fractionated radiation therapy is often effective in at least temporary control of the primary site. Both of these modalities are associated with minimal morbidity and because of that many owners are comfortable pursuing these treatment options.
Squamous cell carcinoma accounts for ~70% of oral tumors in the cat. It is often mistaken for severe dental disease early in its clinical course. The median survival time without treatment is in the range of two months and any single treatment modality is unlikely to impact that number unless it is a very small tumor that can be removed aggressively. NSAID's with cox-2 inhibition may slow these tumors down and make the patients more comfortable but significant clinical responses and long term survival are uncommon. Toceranib (Palladia) may also have some activity. A combination of radiation therapy and mitoxantrone has been reported to increase survival times. Multi-modality therapy will be essential to controlling these tumors, but the optimum combination remains unknown at this time and their prognosis remains extremely guarded. The only other tumors noted with any frequency are fibrosarcomas and malignant melanomas. No data exists to indicate whether the melanoma treatment vaccine has any activity in the cat.
These can arise from sebaceous or apocrine glands and are relatively common in the dog but rare in the cat (cats do not have perianal sebaceous glands). Sebaceous cells of the perineum are described as 'hepatoid' on cytology and perianal adenomas are very common in intact male dogs. They are highly testosterone dependent, and neutering the dog will often result in significant resolution of the masses. Malignant sebaceous gland tumors may be very difficult to distinguish on cytology alone and should always be considered in more invasive, ulcerated lesions. Serial surgical resections are often possible in these tumors and doxorubicin and cisplatin have both been documented to have activity.
Apocrine gland adenocarcinoma of the anal sac (AGASACA) is noted with equal frequency in male and female dogs. Metastasis to regional lymph nodes is documented in greater than 50% of cases. Hypercalcemia is noted in ~27% of cases and clinical signs secondary to the hypercalcemia may be the presenting clinical signs (polydipsia, polyuria, anorexia, lethargy, weakness). Keep in mind that the primary site in the anal sac may be very small. This is a tumor where the more aggressively they are treated, the longer the survival time. With surgery alone reported survival times are in the range of one year. The addition of chemotherapy will extend survival times by a few months. The addition of radiation therapy and chemotherapy will double the medians out to ~2 years. Data recently collected indicates that toceranib (Palladia) may also have activity in this disease. The presence of hypercalcemia has been associated with a poorer prognosis.