It is considered that cancer stem cells have the same characteristics as normal stem cells, such as drug-resistance, self-renewal, differentiation, and tissue-formation. Normal stem cells depend on their surroundings, a niche. Cancer stem cells may also depend on their own niche. Because cancer stem cells are resistant to present remedies, it is important to find a remedy targeting cancer stem cells. The remedy must not only target cancer stem cells themselves but also target the niche surrounding the cancer stem cells.