Introduction

Canine melanomas have diverse biologic behaviours, depending on several factors including size, site, stage, histopathological characteristics. Oral, digital and some cutaneous melanomas (including muco-cutaneous junction) may carry a poor prognosis, due to local invasiveness and high metastatic propensity. Median survival time (MST) of dogs treated with surgery and/or radiotherapy is of approximately 12 months (range 3–19) with most dogs dying of metastatic disease. In the USA a commercially available xenogeneic DNA vaccine administered in dogs with locally controlled tumours has increased survival times. The purpose of this study is to report the efficacy of this vaccine in dogs with naturally occurring MM in the UK.

Methods

Medical records of two institutions were retrospectively reviewed. Dogs with clinical and histopathological diagnosis of aggressive MM, which received at least one dose of melanoma vaccine were included. Kaplan-Meier product limit estimation for overall survival and Cox proportional hazards regression for potential prognostic factors were performed.

Results

Twenty-five dogs were included in the study; Retrievers were overrepresented (40% of the study population). The median age was 9.8 years (range 5.5–16.0); there were sixteen males and nine females. Seventeen tumours were localised in the oral cavity and eight were non-oral MM. Tumour size was recorded for 24/25 dogs, ranging from 2 to 100 mm (major dimension). Eleven tumours were amelanotic and seventeen had MI > 3/10hpf. All dogs underwent surgery of the primary tumour (eighteen incomplete margins). Seven dogs received adjuvant radiotherapy and sixteen dogs received systemic treatment. Local tumour control prior to vaccine was achieved in twenty-one cases. Six dogs presented with metastatic disease at different sites (4 lymph node, 3 lung, 1 eye) prior to immunotherapy.

One-hundred and fourteen doses of vaccine were administered (range 1–8, median 4.5). Vaccine-related side effects were reported in 7 dogs, which included lethargy, panting, insomnia, vomiting, pain at injection site, lameness, hair discoloration.

The MST for all dogs was 666 days (95% C.I. 149–1183 days). Eleven dogs were still alive at the end of the study, seven were disease free. WHO stage for oral tumours and distant metastases at diagnosis were the only statistically significant prognostic factors. No dogs were lost to follow up.

Conclusions

These data suggest that melanoma vaccine is a well-tolerated treatment, which prolongs the MST of dogs with MM in the UK.