Vascular endothelial growth factor (VEGF) is a key regulator in both physiologic and pathologic angiogenesis, and cannabinoids decrease VEGF release in human and murine cancer cells. The aim of this study was to assess the in vitro effects of a synthetic cannabinoid, WIN-55,212-2, on the expression of the proangiogenic factor VEGF-A in the canine osteosarcoma cell line 8. After analysis of gene expression by quantitative real-time polymerase chain reaction, the compound decreased VEGF-A expression by 35% ± 10% (P , 0.0001) as compared with the control. This synthetic cannabinoid shows promise as a potential inhibitor of angiogenesis, and further studies are warranted to investigate its in vivo effects and to explore the potential of this and related compounds as adjuvant cancer therapy in the dog.