The most common oral tumours in dogs and cats
NEW ORLEANS, LA – Oral tumours are common in dogs and cats and their incidence increases with age. The most common malignant oral tumours in dogs are melanoma (OMM), fibrosarcoma (FSA), and squamous cell carcinoma (SCC), with SCC being the most common in cats. Presenting complaints can include a visible mass, bloody or increased saliva, pawing at the face, loose teeth, gingival proliferation or bleeding, facial deformity, weight loss, gagging, dropping food out of the mouth, and less commonly, enlarged mandibular lymph nodes or salivary glands or exophthalmos. A thorough oral exam should be part of every physical exam, explained Tracy Gieger, DVM, DACVIM, DACVR, speaking at the ACVIM Forum. This includes lips, cheeks, tongue/sublingual region, salivary glands, palate, teeth, and tonsils. Dr. Gieger added that she recommends performing an oral examination on any anesthetized/intubated patient.
Canine oral tumours
Oral malignant melanoma (OMM) can be locally invasive causing bone destruction and regional lymph node and distant metastasis. Melanomas on the lip are usually less malignant than those inside the oral cavity. Aspiration of a pigmented OMM or metastatic lymph node yields fluid that is black. Complete systemic staging is recommended for dogs with OMM, and if staging is negative for metastasis, aggressive local therapy should be considered. Dr. Gieger said that since OMM is likely to metastasize, options such as the Merial® melanoma vaccine or possibly chemotherapy should be considered as an adjunct treatment. Many dogs with non-resectable melanomas can be managed with radiation therapy (RT); about 75% of dogs will have a response to RT, but most ultimately die of metastasis within 6-9 months. If dogs with OMM present with visible metastasis, the prognosis is poor since chemotherapy drugs are minimally effective in treating gross metastatic disease. Chemotherapy drugs that may have efficacy against melanoma include carboplatin, dacarbazine, lomustine, and melphalan.
Oral squamous cell carcinoma (SCC) in dogs typically appears as an erosive or proliferative mass, and sometimes as an oronasal fistula. This tumour is locally invasive and sometimes metastasizes to the regional lymph nodes. If staging for metastasis is negative, aggressive local therapy is warranted. Surgical resection of the primary tumour is often possible with partial mandibulectomy or maxillectomy, but if surgery is not an option due to size or location of the tumour, RT may help to control the local disease. Non-steroidal drugs may also be helpful in symptomatic therapy and possibly anti-tumour effects. If complete removal with surgery is achieved, long-term tumour control is possible. Dr. Gieger said that follow-up chemotherapy is rarely warranted and has not been shown to be definitively effective in treating or preventing metastatic disease. In most studies of dogs with SCC treated with combinations of surgery and/or radiation therapy, median survival times are approximately 1-1.5 years.
Fibrosarcoma of the oral cavity is typically locally invasive with a bland histologic appearance and lack of metastasis. These tumours are most commonly seen on the maxillae of Golden retrievers but can be seen in other breeds and in other locations within the oral cavity. They are often mistaken for “benign” swellings or trauma to the face, and cytology often produces false negative results. Often, incisional biopsies reveal only inflammatory cells/fibrous connective tissue. It is common for these tumours to invade into the nasal cavity, orbit, and sometimes brain. A recent study showed that with aggressive local resection, 88% of dogs were alive one year after surgery. Radiation therapy is useful to slow the progression of non-resectable tumours, but cure is unlikely; RT typically controls tumour growth for 6-9 months before progression. Chemotherapy may be useful for palliation, but rarely provides long-term control.
Feline oral tumours
Oral tumours make up 10% of all feline tumours, most often in cats older than 15 years of age, and they are frequently associated with significant morbidity because they are not detected until late in the course of the disease. SCC makes up the majority of feline oral tumours, and other less common tumours include lymphoma, fibrosarcoma, melanoma, and mast cell tumours.
Cats that live in smoking households are twice as likely to develop this type of cancer. The use of flea collars and a canned food diet have also been implicated as risk factors for SCC development. These tumours are usually sublingual or mandibular in location, but can be maxillary or pharyngeal. In some cats, a palpably thickened mandible without evidence of a soft tissue tumour is sometimes seen. Bone lysis is common, and dental radiographs should be performed in any cat with loose teeth or gingival proliferation. Most SCC cannot be surgically resected due to their location. If surgery is possible, it is often the cat’s best chance for long-term survival. For sublingual and other non-resectable tumours, RT often helps to decrease inflammation and improve pain control. For cats that are relatively healthy besides the tumour, RT is usually the best option; the median survival time for cats with SCC treated with RT is approximately four months. Chemotherapy is rarely helpful in the management of this tumour.
Staging for oral tumours
Staging should include 3D measurement of the tumour with calipers and drawing/recording the tumour on a body map or oral cavity exam form. Fine needle aspiration and cytology can be performed, but Dr. Gieger cautioned that secondary inflammation and sometimes infection can be present, possibly causing a false negative for the diagnosis of a tumour. Regional lymph nodes should always be aspirated if they are accessible, even if they are normal in size. Bloodwork should be performed to examine for evidence of systemic disease prior to anesthesia or therapy for oral tumours. All cats with oral tumours should be FeLV/FIV tested. Thoracic radiographs should be considered in any patient with a malignant oral tumour. Abdominal imaging should be considered in older patients prior to aggressive local therapy for oral tumours to stage them for evidence of systemic disease.
Skull and/or dental quality radiographs can be useful to examine the underlying bone for lysis, and are more useful for mandibular tumours than maxillary tumours. Computed tomography (CT) or magnetic resonance imaging (MRI) can be useful to detect bony lysis, to determine the extent of the tumour, and to examine all of the regional lymph nodes for evidence of neoplasia. CT is useful for radiation therapy treatment planning, and both CT and MRI are useful in surgical planning.
Obtaining a diagnosis and other biopsy-related information prior to contemplating a definitive treatment plan is helpful, especially for tumours where complete surgical excision is not possible.
In general, the prognosis is best for rostrally-located tumours, tumours less than 2 cm, and tumours without bony lysis and/or regional lymph node involvement. As with any tumour type, early diagnosis and appropriate therapy provides the best chance for long-term tumour control.
Symptomatic care
Antibiotic therapy is almost always warranted; choices include clindamycin and amoxicillin-clavulanic acid. Long-acting antibiotics such as cefovecin may be useful in such patients as well. Anti-inflammatory medications such as NSAIDs or steroids (not to be given concurrently) are usually indicated in patients with oral tumours to alleviate inflammation/discomfort. Other pain medications including tramadol and other opiates may be indicated in some patients, and oral rinses may help to keep the mouth moist and decrease food and saliva buildup around a tumour. CVT
