PROBLEM TO BE SOLVED: To provide an antitumor agent which is effective against a tumor having invasive or metastatic potential. An antitumor agent containing a SNORA23 gene expression inhibitor is disclosed. The SNORA23 expression inhibitor is an oligonucleotide containing at least one nucleoside structure represented by the following formula (I): embedded image (where Base and A are predetermined substituents or structures), or a pharmacology thereof. It may be an acceptable salt. Anti-tumor agents including SYNE2 gene expression inhibitors are also disclosed. [Selection diagram] None【課題】浸潤性または転移能のある腫瘍に対して有効な抗腫瘍剤を提供すること。【解決手段】ＳＮＯＲＡ２３遺伝子発現抑制剤を含む抗腫瘍剤が開示される。ＳＮＯＲＡ２３発現抑制剤は、以下の式（Ｉ）で表されるヌクレオシド構造： 【化１】（式中ＢａｓeおよびＡは所定の置換基または構造である）を少なくとも１つ含むオリゴヌクレオチドまたはその薬理学上許容される塩であり得る。ＳＹＮＥ２遺伝子発現抑制剤を含む抗腫瘍剤もまた開示される。【選択図】なし
