Page 86 - WSAVA2018
P. 86

 25-28 September, 2018 | Singapore
Surgery:
General surgical oncologic principles apply and oral tumours should be removed via wide en bloc surgical resection. For oral tumours associated with the maxilla or hard palate, this will be achieved by maxillectomy which can be partial or a complete hemimaxillectomy. Closure of the resultant oronasal defect is by a local mucosal flap raised from the ipsilateral gingiva. Most dogs have god to excellent functional outcomes and minimal cosmetic changes. Mandibular tumours require mandibulectomy (rostral, segmental or hemi). Post operatively, some animals experience ‘mandibular drift’ where the mandibular teeth do not align with the maxillary teeth. Cats can undergo mandibulectomy or maxillectomy but often require a longer period of adaption after surgery and oesophageal feeding tubes are required to provide nutrition in the post-operative period.
Removal of the draining lymph nodes is recommended in cases of oral tumours to provide accurate staging information. A recent description of a technique to remove all three draining lymph nodes through a single ventral cervical access incision has been published.
Lingual tumours can be treated by partial or subtotal glossectomy. The tongue is very vascular so appropriate haemostatis is required during surgery. If major glossectomy is required (e.g. for large or caudally located tumours), then the owners should be aware of the management and morbidity concerns before undertaking such a procedure.
Tonsillar tumours are most commonly SCC. They can be removed by tonsillectomy which is made easier with the use of a vessel sealing device. Surgery is considered palliative in these cases as tonsillar SCC is a highly metastatic and aggressive disease in dogs.
Following surgery, adjunctive therapy should be considered from two aspects - the need for additional local control due to narrow or incomplete histologic margins and the need for systemic therapy due to risk of metastasis. From a local control standpoint, assuming an aggressive first surgery has been performed,
as discussed above, more extensive surgery is not generally possible in the oral cavity. Local recurrence can occur despite apparently complete excision (approx. 15-20% in canine oral tumours in general), but is very common following incomplete excision (>60%), and recurrent disease negatively impacts survival time. In the specific cases of feline oral SCC and canine oral FSA, local recurrence may be more common than other oral malignancies. In general, local recurrence is less common for mandibular tumours than maxillary tumours, likely due to the ability to obtain wider margins. Local recurrence is also greater for larger tumours, again likely due to incomplete excision. Where additional local control is indicated, radiation therapy (RT) is often very
effective. With aggressive local therapy, outcomes for SCC and FSA in dogs can be very good, with median survival times of greater than 1.5-2 years (SCC generally better than FSA). Acute side effects from RT in the
oral cavity are common but typically manageable with aggressive analgesia, and generally resolve within a few weeks. Feeding tubes may be required in some patients.
Adjuvant systemic therapy after local therapy is generally not indicated for canine oral SCC and FSA as they
do not typically cause distant metastasis (varies with
the study). If lymph node metastasis is documented, adjuvant chemotherapy may be warranted. In contrast, oral melanoma in dogs is considered to have a high
risk of metastasis. The local disease (primary tumour
+/- LN) can often be effectively controlled with surgery and/or RT, but development of metastasis is common. Systemic therapies including chemotherapy (carboplatin, dacarbazine, temozolomide) and immunotherapy (Oncept and other vaccines) have not shown a statistically significant improvement in survival over local therapies alone. Small tumours (< 2cm) may have fair
to good outcomes with aggressive local therapy alone (median 1.5-2 years compared to 6-8 months for larger tumours).
For tumours where surgical excision is not possible, radiation therapy is generally the preferred option. Canine oral melanoma tends to be very radiation responsive. Hypofractionated/palliative type protocols are generally recommended for melanoma. As discussed above, although the local tumour can be effectively controlled, metastasis is common. There is some information about RT as sole treatment for canine SCC, with median control time of approximately 1 year reported with definitive-type protocols, though this may be better in smaller tumours. Canine FSA is generally thought to be less radiation responsive, though median control of 10 months is reported in one study. Palliative RT can be considered for any painful oral tumour.
Chemotherapy could be considered for macroscopic oral tumours if surgery and radiation are not feasible, or for metastatic tumours, however evidence of efficacy
is sparse. Canine oral melanoma may respond to platinum agents, and dacarbazine & its related drug temozolomide have shown some efficacy in melanoma in humans. The Oncept melanoma vaccine may also have some benefit in some dogs, with occasional responses reported in macroscopic disease. There may be a potential benefit to combining Oncept with metronomic chemotherapy either in the adjuvant setting or with macroscopic melanoma. For canine oral SCC, responses are reported to carboplatin and piroxicam in some dogs, toceranib (+/- NSAID +/- cyclophosphamide), and even piroxicam alone. Canine oral FSA is likely to be relatively chemoresistant given responses of macroscopic soft tissue sarcomas in general, though some response to
  84
43RD WORLD SMALL ANIMAL VETERINARY ASSOCIATION CONGRESS AND 9TH FASAVA CONGRESS














































































   84   85   86   87   88