Immunohistochemical analysis was made using an extended panel of endothelial markers, including Erythroblastosis Transformation-Specific Regulated Gene (ERG) and caveolin-1 (Cav-1), which, to the authors' knowledge, have not previously been applied in feline vascular tumors, in addition to von Willebrand Factor (vWF) and α-smooth muscle actin (α-SMA). The gene discussed is ACTA1; the disease is vascular neoplasm.