A method and medicament comprising 4,4,4-trifluoro-N-[(1S)-2-[[(7S)-5-(2-hydroxyethyl)-6-oxo-7H-pyrido[2,3-d][3]benzazepin-7-yl]amino]-1-methyl-2-oxo-ethyl]butanamide or a pharmaceutically acceptable salt or hydrate thereof for treating leiomyosarcoma is provided.本發明提供一種用於治療平滑肌肉瘤之方法及藥劑,其包含4,4,4-三氟-N-[(1S)-2-[[(7S)-5-(2-羥乙基)-6-側氧基-7H-吡啶并[2,3-d][3]苯并氮呯-7-基]胺基]-1-甲基-2-側氧基-乙基]丁醯胺或其醫藥學上可接受之鹽或水合物。