The invention provides a method of treating an IGF-activated tumour in a subject in need of such treatment, said method comprising administering to said subject an effective amount of an expression cassette comprising a polynucleotide encoding an IGFBP4 (Insulin-like Growth Factor Binding Protein 4) polypeptide operably linked to a muscle-specific regulatory element, such that said polynucleotide is expressed in said tumour to form said polypeptide.
