Abstract: The present invention relates to vectors for cancer therapy which as a result of genetic differences between normal and transformed cells selectively eliminate the latter. This is made possible by integrating a sequence-specific recombinase into a viral or non-viral expression vector whose expression is controlled by a transcription factor which has mutated in tumor cells and is therefore inactive, and also by a suicide gene which is flanked by at least one recombinase-specific target sequence. Through the transcription factor-mediated activation of the sequence-specific recombinase the vector is eliminated from untransformed cells together with the suicide gene. The vector is, however, not eliminated from tumor cells in which the transcription factor is inactive, and expresses the suicide gene. After contact with a corresponding prodrug these cells are selectively killed off.