The invention relates to the use of a product selected from: (i) a protein containing the amino acid sequence shown in SEQ ID NO:1 and associated with the viral protein A238L or a functionally equivalent fragment or variant thereof; (ii) a polynucleotide encoding said protein, variant or fragment; (iii) a gene construction containing said polynucleotide; (iv) a vector containing said polynucleotide or gene construction; and (v) a host cell containing said polynucleotide, gene construction or vector, in the preparation of an anti-tumour pharmaceutical composition for the treatment and/or prevent of tumours and cancer.