Canine Nasal Tumours

by

Chapter: Discussion

Tumors of the nasal cavity and paranasal sinuses are uncommon, accounting for approximately 1-2% of reported canine neoplasms (Madewell et al., 1976:49). The most common primary nasal tumor cell type is adenocarcinoma in dogs. Regardless of the tumor histologic type, invasion of surrounding structures is common, however distant metastasis is infrequent (Madewell and Theilen, 2002:240). Causes of companion animal nasal cavity neoplasia have not been specifically determined, but evidence suggests a potential relationship to environmental pollutants ( [Hayes et al., 1981:188] and [Dahl et al., 1982:154]).

Though radiography and patient history may be highly informative, a definitive diagnosis of nasal neoplasia requires a tissue biopsy (Lana and Withrow, 2001:167). Nasal and sinus radiographs are useful to define the disease extent, to provide a presumptive diagnosis and prognostic impression, and to locate an area within the nasal cavity most likely to yield diagnostic material from a biopsy ( [Gibbs et al., 1979:175] and [Morris et al., 1996:229]). Computed tomography is useful for more accurate tumor detection and staging, defining appropriate biopsy sites, predicting possible treatment-related complications, evaluating tumor regression, and planning of surgery and radiation therapy (Thrall et al., 1989).

Therapy of nasal neoplasia is directed primarily at local disease control. Although surgical debulking has been recommended, its high rate of acute and chronic morbidity, without documented significant extension of life, limits it applicability to palliative status unless other therapies such as radiation are not available ( [Madewell et al., 1976:144], [MacEwen et al., 1977:105] and [Henry et al., 1998:75]). Brachytherapy, immunotherapy, cryosurgery, and chemotherapy have also been used for nasal tumor treatment. However, the efficacy for extension of survival was questionable, and shortcomings were associated with these treatment approaches ( [MacEwen et al., 1977:18], [Withrow, 1982:177], [White et al., 1990:105] and [Hahn et al., 1992:698]). A number of reports from various veterinary institutions describing the efficacy of radiation therapy for nasal tumors are available ( [Norris, 1979:105], [Thrall and Harvey, 1983:244], [Adams et al., 1987:187], [Evans et al., 1989:10], [McEntee et al., 1991:166], [Theon et al., 1993], [Thrall et al., 1993:185], [Henry et al., 1998:174], [Adams et al., 1998:414], [LaDue et al., 1999:130], [Northrup et al., 2001:155], [Mellanby et al., 2002:164] and [Correa et al., 2003]). These reports suggest a number of therapeutic approaches and protocols. In general, despite variations due to specific tumor cell types, the type of radiation used, and the various treatment protocols, there was agreement that irradiation of canine nasal tumors prolonged survival. The use of radiotherapy in the treatment of nasal neoplasms increases survival time compared to animals treated by other modalities (Henry et al., 1998:209). With the exception of one multi-institutional study (Rassnick et al., 2006:188), minimal survival data was available on animals that were not treated using any modality to compare to those receiving radiotherapy with or without surgery or chemotherapy (MacEwen et al., 1977:374).

The tumor cell-type did not have any statistically significant relationship to survival across irradiated or non-irradiated dogs. Whether this truly indicates that tumor cell type does not matter, or ...