Introduction

Canine oral malignant melanoma (OMM) is a locally aggressive oral tumor with high risk of locoregional and distant metastasis. With multimodal therapy, most dogs will succumb to OMM within 1–2 years. Locoregional therapy typically includes surgery, radiation therapy (RT), or a combination thereof. Current practice patterns favor the use of hypofractionated RT. One commonly used protocol is 6 Gy x 6 fractions; however, this protocol is not well-described. Thus, the objective of this tri-institutional retrospective study was to describe oncologic outcomes.

Methods

Dogs were included in the analysis if they underwent 6 Gy x 6 irradiation to manage micro- or macroscopic OMM. Progression-free and overall survival times were characterized using Kaplan-Meier statistics and Cox regression modeling. Univariate analyses were performed to assess the prognostic value of various factors including dose intensity (weekly vs. biweekly; n=57 and 44, respectively), treatment planning type (manual vs. computerized; n=44 and 48, respectively, 9 unknown), treatment of micro- or macroscopic disease (n=36 and 65, respectively) and tumor stage.

Results

For the entire group (n=101 dogs), the median progression-free survival and overall survival times were 171 and 232 days, respectively. Based upon univariate analysis, variables that were statistically significantly (p<0.05) included: presence of macroscopic disease (p≤0.0001), bony lysis (p=0.0253), advanced tumor stage (p=0.0079), and metastasis at diagnosis (p=0.0002).

Conclusion

The final statistical model (Cox multivariable regression) will be built upon completion of data collection.