In the present study, we used tumor-selective replicating adenovirus expressing IL-24 (ZD55-IL-24) which deleted the essential viral E1B 55 kDa gene and exerted a strong cytopathic effect and significant apoptosis in tumor cells without normal cells [15] to further explore the mechanism of MDA-7/IL-24 inducing Bcl-2 down-regulation and subsequent carcinoma cell apoptosis. This evidence concerns the gene BCL2 and neoplasm.