The present invention provides a method of screening an agent for the prevention/treatment of cancer. More specifically, the present invention provides a screening method/screening kit for screening a compound or its salt that changes the binding properties of a protein comprising the same or substantially the same amino acid sequence as the amino acid sequence represented by SEQ ID NO: 1, or salts thereof, to a ligand capable of binding specifically to the protein, which comprises using (a) the protein, its partial peptides, or salts thereof and (b) the ligand capable of binding specifically to the protein; compounds obtained by the screening or salts thereof; agents for the prevention/treatment of cancer comprising the compounds or salts thereof; and so on.