E2F1 and neoplasm: Based on the preclinical and clinical findings reported here, Ad5/3-E2F-Δ24-GMCSF seems to function as designed: The Ad3 fiber knob enables efficient transduction of tumor cells while the E2F1 promoter and 24bp deletion provide excellent tumor selectivity (as demonstrated by lack of replication in hamster livers in vivo and human hepatocytes ex vivo).