PROBLEM TO BE SOLVED: To provide a cancer stem cell isolated using a cellular marker, a substantially uniform cancer stem cell population comprising the cancer stem cells, and a method for producing the cancer stem cell population.SOLUTION: According to the present invention, there are provided cancer stem cells of mesenchymal cells positive to a cell marker Lgr5 and adherent in a serum-free culture； cancer stem cells of epithelial cells are positive to Lgr5 and free-floating in a serum-free culture； a method for producing a cancer stem cell population in which these are gastrointestinal cancers (colon cancer)； a method for screening a pharmaceutical product using the cancer stem cell or the cancer stem cell population； and a method for detecting/identifying or quantifying the presence of the cancer stem cell or cancer stem cell population.SELECTED DRAWING: None【課題】細胞マーカーを用いて分離された癌幹細胞であって、該癌幹細胞を含む実質的に均一な癌幹細胞集団、該癌幹細胞集団の製造方法を提供。【解決手段】細胞マーカーのＬｇｒ５が陽性で無血清培養で付着性の間葉性細胞の癌幹細胞。Ｌｇｒ５陽性で無血性培養で浮遊性の上皮細胞の癌幹細胞。これらが消化器癌（大腸癌）である癌幹細胞集団の製造方法。更に、上記癌幹細胞又は上記癌幹細胞集団を用いた医薬品のスクリーニング方法、上記癌幹細胞又は癌幹細胞集団の存在を検出・同定又は定量する方法。【選択図】なし
