Efficacy and side effects of radiation therapy in comparison with radiation therapy and temozolomide in the treatment of canine malignant melanoma.

Introduction. In dogs, malignant melanoma (MM) is notorious for its propensity to metastasize and for its poor response to current therapeutic regimens. Better tolerated, less toxic, and more efficacious treatments are needed. Material and methods. Dogs with newly diagnosed or recurrent, histologically confirmed MM of any clinical stage were prospectively enrolled to investigate objective response, time to progression (TTP), and overall survival as well as the safety profile of radiation therapy (RT) in comparison with RT and temozolomide. The RT protocol consisted of 5 fractions of 6 Gy to a total dose of 30 Gy over 2,5 weeks. Dogs whose owners wished to pursue chemotherapy received adjuvant oral temozolomide (60 mg/m2/die for 5 days). Treatment cycles were repeated every 28 days for 4 cycles. Results. Fifteen dogs were treated with RT (Group 1) and 11 dogs were irradiated and subsequently treated with temozolomide (Group 2). Response rate was 73.3% (3 complete remissions [CR], 8 partial remissions [PR]) in Group 1, and 72.7% (2 CR, 6 PR) in Group 2. Median TTP was not significantly different among groups. When considering survival time, dogs in Group 2 lived significantly longer than dogs in Group 1 (p = 0.094). Toxicity was similar between groups. Conclusion. Conventionally fractionated RT followed by 4 cycles of temozolomide has a good safety profile and increases survival time in dogs with MM. These results warrant future randomized trials to further explore the role of adjuvant temozolomide, and support the general concept of combining radiation therapy with radioenhancing chemotherapeutic agents.