Malignant melanoma is one of the most common and aggressive tumors in the oral cavity of dogs.1–3 Dogs with oral malignant melanoma have poor prognosis because this type of tumor rapidly invades the surrounding tissue and has a high likelihood of regional and distant metastases early in the course of the disease.4,5
Surgery and radiation treatment are the most common methods used to locally control oral tumors. The reported MST for untreated dogs with oral malignant melanoma is 65 days.5 In comparison, the MST for dogs treated by surgery ranges from 9.1 to 9.9 months,6–8 and in dogs treated by radiotherapy alone or in combination with surgery, the MST ranges from 7.0 to 7.9 months.9,10 Owing to these reports of extended survival times, aggressive surgery is the first choice for local treatment of oral malignant melanoma.11 However, a variety of complications such as difficulty eating or aesthetic changes may occur after surgery.12
Oral melanoma responds to hypofractionated radiotherapy in humans and in dogs.9,13–15 Additionally, several prognostic factors that affect radiotherapy outcomes have been identified. Proulx et al10 reported that the overall survival time was longer in dogs without radiographic evidence of bone destruction than in dogs with radiographically evident bone changes. Blackwood and Dobson16 also found that dogs with tumors < 5 cm3 in volume were more likely to achieve a complete response, and they found an association between tumor volume and MST; the MST was 86 weeks in dogs with tumors < 5 cm3, 16 weeks in dogs with tumors between 5 and 15 cm3, and 20.5 weeks in dogs with tumors > 15 cm3 at the time of first treatment. Although Bateman et al9 did not find any association between the clinical stage of cancer and the response to radiotherapy or survival time, that study lacked sufficient case numbers to make a definitive determination.
The purpose of the study reported here was to evaluate the clinical outcomes of dogs with oral malignant melanoma treated by radiotherapy with or without cytoreductive surgery or other adjunctive treatments. We also sought to identify differences in outcomes for dogs that received MVX versus OVX radiotherapy and for dogs with different stages of melanoma according to World Health Organization staging guidelines.
Median survival time
Response evaluation criteria in solid tumors
Asteion Super4 Edition, Toshiba Medical Systems, Tokyo, Japan.
Radioflex 300EMG, Rigaku Corp, Tokyo, Japan.
PRIMUS Mid Energy, Tokyo, Japan.
XiO, version 4.6, Elekta AB, Stockholm, Sweden.
Prism, version 6.01, GraphPad Software Inc, La Jolla, Calif.
JMP, version 10.0.0, SAS Institute Inc, Cary, NC.
Randa Inj, 50 mg/100 mL, Nippon Kayaku Co Ltd, Tokyo, Japan.
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