An inhibitor described in the following (a) or a tumor therapeutic agent containing the nucleic acid described in (b): (a) an miR-151-3p inhibitor, an miR-886-3p inhibitor, or an SMPD3 inhibitor, (B) (1) nucleotides represented by any of miR-29b-1 *, has-miR-221 *, miR-138, miR-584, miR-30a, miR-146a, or SEQ ID NOs: 1-6 A nucleic acid comprising a nucleotide sequence having 70% or more identity to the sequence and having a target gene expression inhibitory activity, or (2) a nucleic acid that is an expression vector capable of expressing the nucleic acid of (1) above.以下の（ａ）に記載の阻害剤、あるいは（ｂ）に記載の核酸を含有する腫瘍治療剤：（ａ）miR-151-3p阻害剤、miR-886-3p阻害剤、またはSMPD3阻害剤、（ｂ）（１）miR-29b-1*、has-miR-221*、miR-138、miR-584、miR-30a、miR-146a、または配列番号１～６のいずれかで表されるヌクレオチド配列と70%以上の同一性を有するヌクレオチド配列からなり且つ標的遺伝子発現抑制活性を有するヌクレオチドを含む核酸、又は（２）上記（１）の核酸を発現し得る発現ベクターである核酸。
