Canine Malignant Melanoma; The effectiveness of a new DNA vaccine

Abstract

Introduction: Canine Malignant Melanoma (CMM) is a very aggressive, potential metastatic neoplasm of melanocytes. They account for 9 to 20% of all skin tumors and occur in dogs that have heavily pigmented skin or oral mucosa. CMM have a high chance of metastasis (51%) even after surgical removal of the primary tumor and adjuvant therapy. The mean survival time for dogs with CMM is 5 to 8 months. Xenogeneic DNA vaccination of dogs with CMM induce an immune response and may increase the survival time significantly. Aim of study: The aim of this study was to investigate the effectiveness of the CMM vaccine. The hypothesis of the study was that the vaccine as a supplementary therapy for CMM would increase the survival of dogs with MM. Materials and methods: Eight dogs with an average age of 9.2 years old were treated with a xenogeneic human tyrosinase vaccine against CMM, after surgical removal of the tumor and radiation therapy. The vaccine was administered 4 times biweekly, and a vaccination boost was suggested to be given 6 months after the last vaccination. After therapy, the dogs visited the surgical oncology policlinic at Utrecht according to a preset protocol. Results: One dog had recurrence of the tumor, one dog had metastasis and one dog developed a recurrence and a metastasis.The mean survival time for these eight dogs was 109 days. There was no increase in survival time observed, compared to the survival times described in literature with conventional treatment. One WHO stage 3 dog had a survival time of 132 days end died at the end of the study. Discussion: Eight dogs diagnosed with CMM were treated with xenogeneic human tyrosinase after surgival removal and radiotherapy. Three dogs had recurrence and/or metastasis of the primary tumor. No increase in survival time was observed in this study and no side effects were observed among the dogs. An explanation for the outcome could be the short study period and the limited number of cases.