PROBLEM TO BE SOLVED: To provide a therapeutic method for treating refractory cancer.SOLUTION: The present invention provides a compound represented by a formula (I) (e.g. tris(8-quinolinolato) gallium(III)) or a pharmaceutically acceptable salt thereof (Ris hydrogen, halogen or sulfono group SOM; M is a metal ion; and Ris hydrogen or, Ris Cl, and Ris I).SELECTED DRAWING: None【課題】難治性癌を治療するための治療方法の提供。【解決手段】式(I)で表される化合物[(例えば、トリス(8-キノリノラト)ガリウム(III)]又はその薬学的に許容される塩。(R1は水素、ハロゲン又はスルホノ基SO3M;Mは金属イオン;かつR2は水素又は、R1がClで、かつR2はI)【選択図】なし