In 2003, Al-Hajj et al. [41] reported that CD44+/CD24−/low Lineage− cells from human breast specimens show a remarkably high tumor-seeding ability, and in 2007, Yu et al. [23] reported that let-7 is a master regulator of CSC properties such as self-renewal activity and tumor-seeding ability. Here, CD44 is linked to neoplasm.