The purpose of the present invention is directed to providing: a detection agent used for specifically detecting a cancer stem cell； a tumor antigenic peptide specifically expressed in a cancer stem cell； a pharmaceutical composition containing the peptide as an active ingredient, which is beneficial for preventing and/or treating a cancer； and a method for screening the tumor antigenic peptide, and the like. In order to achieve the aforementioned purpose, the present invention addresses problems by providing the followings: a peptide represented as Y0-X0-Z0； an antigenic determinant polypeptide which is formed by connecting a plurality of antigenic determinant peptides and includes at least one of the aforementioned peptides as one of the antigenic determinant peptides； a polynucleotide encoding at least one of the aforementioned peptides or antigenic determinant polypeptide； and a pharmaceutical composition containing the peptides/polynucleotide as an active ingredient； a cancer preventing and/or treating agent and the like, which is characterized in that it induces a cytotoxic T cell (CTL).本發明之目的在於提供：一種檢測劑，其用以特異性地檢測癌幹細胞；一種腫瘤抗原胜肽，其被特異性地呈現在癌幹細胞；一種含有此胜肽來作為有效成分之醫藥組成物，其有益於癌症的預防及/或治療；及，一種篩選該腫瘤抗原胜肽的方法等。為了達成上述目的，本發明是藉由提供下述來解決問題：一種胜肽，其是以Y0-X0-Z0表示；一種聚抗原決定基胜肽，其為複數的抗原決定基胜肽所連結而成，並且包含前述胜肽的至少一種來作為抗原決定基胜肽的一種；一種聚核苷酸，其編碼出前述胜肽或聚抗原決定基胜肽的至少一種；及，一種醫藥組成物，其含有該等胜肽/聚核苷酸來作為有效成分；一種癌症的預防及/或治療劑等，其特徵在於會誘導出細胞毒性T細胞(CTL)。
