The invention relates to gene delivery vehicles which comprise nucleic acid molecules encoding apoptosis-inducing proteins VP2 and/or apoptin (VP3) like activity. VP2 and VP3 are viral proteins of the Chicken Anaemia Virus. Also, the invention relates to anti-tumor therapies. Infection of various human tumor cells with the gene delivery vehicles of the invention will result in the induction of apoptosis in tumor cells and much reduced apoptosis, if at all, in normal diploid, non-transformed/non-malignant cells. Also the invention relates to the diagnosis of cancer, and related forms of hyperplasia, metaplasia and dysplasia.