The present invention provides a pharmaceutical composition containing, as an active ingredient, a compound that specifically binds to KSRP or a functional fragment thereof, and a screening method for the compound. KSRP is a novel target protein for anticancer agents; a compound capable of regulating the expression and activity of such a protein and a pharmaceutical composition containing it are highly useful for proliferative diseases, particularly as anticancer agents. By providing the novel target protein, the mechanism behind the anticancer effect that has conventionally been unexplainable can be elucidated.