The present invention relates to an agent for potentiating an antitumor activity of a chemotherapeutic agent against a cancer containing cancer stem cells, which contains at least one kind of branched chain amino acid selected from isoleucine, leucine and valine, or a salt thereof. In addition, the present invention relates to an agent for treating a cancer containing cancer stem cells, which contains a combination of a chemotherapeutic agent and at least one kind of branched chain amino acid selected from isoleucine, leucine and valine, or a salt thereof. Furthermore, the present invention relates to an agent for preventing metastasis or recurrence of a cancer containing cancer stem cells, which contains a combination of a chemotherapeutic agent and at least one kind of branched chain amino acid selected from isoleucine, leucine and valine, or a salt thereof.本發明係關於一種對包含癌幹細胞之癌用以增強化學療法劑之抗腫瘤活性之劑，其係含有由異白胺酸、白胺酸及纈胺酸中選出之至少一種支鏈胺基酸或其鹽。又，本發明係關於一種用以治療包含癌幹細胞之癌之劑，其係使由異白胺酸、白胺酸及纈胺酸中選出之至少一種支鏈胺基酸或其鹽；與化學療法劑組合而成。進一步地，本發明係關於一種用以預防包含癌幹細胞之癌的轉移或復發之劑，其係使由異白胺酸、白胺酸及纈胺酸中選出之至少一種支鏈胺基酸或其鹽；與化學療法劑組合而成。
