A non-human transgenic mammal whose genome comprises a transgene, which transgene comprises a promoter operably linked to a DNA fragment, wherein: the promoter comprises the nuclear factor binding region of the RR2 cis acting element of an FGF1B promoter; the DNA fragment comprises a sequence encoding the SV40 large T antigen; and the mammal comprises a tumor, the cells of which lack immunodetectable levels of glial fibrillary acidic protein, S-100, synaptophysin and neuron-specific enolase. Such a transgenic animal may be used in screening method for the identification of therapeutic agents useful in brain or tumor therapy.
