This invention provides an antitumor drug delivery formulation for treating a subject having a tumor more highly expressing a TUG1 gene than normal tissues or preventing the subject from tumor metastasis, comprising a polymeric micelle comprising a nucleic acid that suppresses high expression of the TUG1 gene as an active ingredient, wherein the polymeric micelle comprises a block copolymer having a cationic poly(amino acid) segment and a hydrophilic polymer chain segment and the nucleic acid, and wherein the nucleic acid is bound to a cationic group of the cationic poly(amino acid) segment to form a complex and/or the nucleic acid is incorporated in the micelle or attached into the micelle; and the polymeric micelle accumulates in the tumor.