CD34 and neoplasm: AdvGFP/MDA-7 treatment significantly down-regulated the expression of VEGF and CD34 in tumors infected with AdvGFP/MDA-7 compared with those infected with AdvGFP and PBS (Fig. 6, P < 0.05), suggesting that down-regulation of VEGF and CD34 expression was a possible mechanism whereby AdvGFP/MDA-7 inhibited tumor growth in vivo.