Preoperative Planning and Staging

An operative plan is made before surgery. This is based on comprehensive staging (e.g., thorough physical/oral examination, thoracic radiographs, abdominal radiographs and/or ultrasonographic evaluation, computed tomography (CT) (or skull radiographs for rostral lesions), biopsy results from the mass and cytology of the associated lymph nodes. The biological behaviour of the tumour is reviewed. If advanced resection or reconstruction is required (as for most large or caudal maxillary tumours), or if special equipment or postoperative management will be required, referral to a specialty practice may be prudent.

Communication between surgeons, medical oncologists and radiation therapists is essential as well as clear communication with the owners. To avoid interference with wound healing, surgery should be performed either prior to, or between 2 and 6 weeks after radiotherapy, and chemotherapeutics should not be administered for 7 days before or after surgery.

Preoperative Management

Concurrent disease must be diagnosed before anaesthesia and surgery. Many animals with cancer are older in age and may have heart, kidney, liver or other organ disease. Preoperative adjuvant therapy may affect organs such as the kidneys (e.g., cisplatin) or heart (e.g., adriamycin). Cancer cachexia from poor intake and utilisation of nutrients may depress the immune system and inhibit wound healing. Placement of feeding tubes prior to or during surgery should be considered, particularly if an aggressive/large resection is being planned. Large resections result in more tension at the suture line and an increased risk of incisional dehiscence. Feeding via a gastrostomy or oesophagostomy tube may decrease this risk in the postoperative period. In addition, animals may not attempt to eat for several days after the resection of a large oral tumour.

Diagnosis and Staging

Oral tumours account for 6% of canine tumours and are the fourth most common canine cancer. Oral tumours account for 3-10% of feline tumours and over 90% of them are malignant (chiefly squamous cell carcinoma). Oral tumours commonly arise from the gingiva in dogs and gingiva or tongue in cats, although they can arise from buccal mucosa, mandible, maxilla, palate, dental structures and tonsils.

Malignant melanoma (MM), fibrosarcoma (FSA) and squamous cell carcinoma (SCC) are the most common oral tumours in dogs, accounting for about 60% of oral tumours in dogs. The other 40% is chiefly made up of the epulides and odontogenic tumours (the nomenclature of these is confusing in the literature). SCC and FSA are the most common oral tumours in cats, accounting for about 90% of feline oral tumours.

Oral tumours are usually proliferative and may be ulcerative. Clinical signs in dogs include decreased appetite, halitosis, tooth loss, bloody salivation, exophthalmos, epistaxis, dysphagia and difficult and painful mastication. Clinical signs in cats include facial asymmetry, ptyalism, anorexia, sneezing, nasal discharge, pawing at mouth, changed eating habits, oral hypersensitivity, loose teeth, dysphagia, weight loss and halitosis.

It is important to perform a thorough oral examination, accurately noting the intra-oral extent of disease. This should be performed in a well sedated animal and usually at the same time as a biopsy. Oral examination should be repeated prior to performing surgery to determine whether the extent of the tumour has altered since diagnosis. Note that because many oral tumours are very large by the time they are diagnosed, teaching your clients how to examine the oral cavity of their pet on a routine basis is a good idea.

Biopsy is required for diagnosis and differentiation of inflammatory and neoplastic tissue. Intraoral biopsy should be performed to avoid tumour seeding in skin and increasing surgical margins. Biopsy is often possible in the conscious animal if the tumour is ulcerated or an exophytic mass. Large incisional biopsies should be performed as oral tumours are often infected, inflamed or necrotic and a small biopsy specimen may misrepresent the underlying disease. Biopsies should be located at the edge and centre of the lesion to increase diagnostic yield. The biopsy site should be planned to minimise contamination of normal tissue. Cytological preparation is usually unrewarding as it is associated with necrosis and inflammation.

The mandibular and medial retropharyngeal lymph nodes receive afferent lymphatics from the head. The mandibular nodes are the easiest to access for fine needle aspiration or biopsy, although ultrasound guidance may be used for the aspiration of deeper nodes. It should be noted that an enlarged node is not necessarily indicative of metastasis, and a palpably normal node does not mean that there is not metastatic disease present. All draining nodes should be aspirated, and any suspicious nodes based on cytology or imaging changes should have biopsies performed prior to treatment of the primary lesion.

Imaging

Intra-oral radiographs can be taken to determine extent of bone lysis, although occasionally the bony reaction is proliferative. It must be remembered that radiographs underestimate extent of bone destruction as lysis is only observed when there is >30-40% cortical bone loss. An absence of radiographic evidence of bone lysis does not indicate the absence of malignant tumour. CT is much more valuable/reliable than radiographs for accurate determination of the local extent of tumour tissue especially in the caudal nasal/oral cavity. Small rostrally situated lesions, especially rostral mandibular tumours, are adequately imaged with high-detail or dental radiographs.

CT imaging is performed to determine the margins of the neoplasm including extent of bone destruction and soft tissue involvement or proliferation into the nasal cavity/orbit/local musculature. Both standard and contrast enhanced studies are performed and evaluated. The resulting three-dimensional reconstruction of the neoplasm aids the surgeon with respect to feasibility surgery and provides a 'map' for the surgical procedure in reference to normal surrounding anatomical structures. When reviewing the CT scan, having a canine/feline skull on hand is quite useful for operative planning.

Treatment of Oral Cancer in Dogs and Cats

Surgery is the mainstay of oral cancer treatment. Surgery is usually the most economical, fast and curative treatment. Mandibulectomy and maxillectomy are usually well tolerated and indicated for bony invasion. Segmental mandibulectomies, large maxillectomies and glossectomies will be described in detail in the lecture.

In oromaxillofacial surgery, attaining tumour-free resection margins is associated with improved prognosis. Often patients present with large, advanced neoplasms, and knowledge of techniques for radical resection are needed to optimise outcome. During the lecture, two radical resection techniques (caudal maxillectomy through a combined approach ± enucleation, and rostral maxillectomy with nasal planum resection) will be shown indicating what is possible, and the functional and cosmetic outcome associated with such surgeries. Given that cosmesis of the face is a concern with pet owners, photographs of animals that have undergone the proposed procedure should be reviewed with them prior to surgery. This is particularly true for large rostral maxillectomies.

Thanks to Dr Duncan Lascelles for contributing heavily to these notes.

References

1.  Lascelles BDX, Thomson MJ, et al. Combined dorsolateral and intraoral approach for the resection of tumors of the maxilla in the dog. Journal of the American Animal Hospital Association 2003; 39: 294-305.

2.  Lascelles BDX, Henderson RA, et al. Bilateral rostral maxillectomy and nasal planectomy for large rostral maxillofacial neoplasms in six dogs and one cat. Journal of the American Animal Hospital Association 2004; 40: 137-146.

3.  Northrup N, Selting KA, et al. Outcomes of cats with oral tumors treated with mandibulectomy: 42 cases. Journal of the American Animal Hospital Association 2006; 42: 350-360.

4.  Schwarz P, Withrow S, et al. Mandibular resection as a treatment for oral cancer in 81 dogs. Journal of the American Animal Hospital Association 1991; 27: 601-610.

5.  Schwarz PD, Withrow SJ, et al. Partial maxillary resection as a treatment for oral cancer in 61 dogs. Journal of the American Animal Hospital Association 1991; 27: 617-624.