DHTKD1 and neoplasm: The tumor specificity of these viruses is achieved by deleting a range of genes including E1B 55KDa or E3 from the viral backbone or by placing the viral immediate early gene E1A gene under the control of a cancer- or tissue-specific promoter and enhancer (PSE, PSA, PSMA, AFP, hTERT, etc.)that is activated in tumor cells.