Safety of administering the canine melanoma DNA vaccine (Oncept) to cats with malignant melanoma - a retrospective study.

Objectives A xenogeneic human tyrosinase DNA vaccine was developed for treatment of dogs with oral malignant melanoma (Oncept; Merial). No studies have evaluated the safety or efficacy of this vaccine in cats. The purpose of this study was to evaluate the safety of the canine melanoma vaccine in cats diagnosed with melanoma. Methods Medical records were reviewed from cats diagnosed with malignant melanoma and treated with the canine melanoma DNA vaccine (Oncept). Data regarding signalment, melanoma location, treatments received, vaccine adverse effects and cause of death were collected. Results A total of 114 melanoma vaccines were administered to 24 cats. Seven cats (11.4%) had clinical adverse effects from a total of 13 vaccines classified as grade 1 or 2 based on the Veterinary Cooperative Oncology Group's common terminology criteria for adverse events v1.1. These included pain on vaccine administration, brief muscle fasciculation, transient inappetence, depression, nausea and mild increase in pigmentation at the injection site. Nineteen cats were deceased at study close. The most common cause of death was melanoma (14 cats). Hematological and biochemical changes were observed in six cats, five of which had concurrent disease or treatments that likely caused or greatly contributed to the laboratory abnormalities found. Therefore, these adverse events were considered unlikely to be caused by the melanoma vaccine. One cat had transient grade 1 hypoalbuminemia, which was possibly caused by the vaccination but not thoroughly evaluated. Conclusions and relevance The canine melanoma DNA vaccine can be safely administered to cats, with minimal risk of adverse effects.