Using mammosphere culture conditions and treatment with anti-cancer reagents, Yu et al. confirmed that CSCs show a CD44+/CD24−/low antigen phenotype and have significant down-regulation of let-7 expression; furthermore, they also demonstrated that let-7 inhibits the self-renewal and de-differentiation of breast cancer cells via direct targeting of the genes encoding RAS and high mobility group AT-hook 2 (HMGA2), respectively. Here, HMGA2 is linked to breast cancer.