Abstract: A viral DNA construct, and virus encoded thereby, is provided having one or more tumour specific transcription factor binding sites in place of one or more wild type transcription factor binding sites operatively positioned in the promoter region which controls expression of early genes responsible for viral nucleic acid replication. Preferred constructs place the tumour specific transcription factor binding sites in operative relation to DNA polymerase, DNA terminal protein and/or DNA binding protein. Compositions and constructs contained therein are provided, particularly for use in therapy. Methods of treating patients for neoplasms are also provided.