Figure 1: A simplified example on the relationship between CSCs and miRNAs with tumor aggressiveness. The miRNA miR-21 is over-expressed in cancers contributing to increased tumor aggressiveness while let-7 miRNA has tumor suppressor effect leading to reduction in tumor aggressiveness, and accumulation of let-7 is prevented by Lin28B, which is over-expressed in many cancers. Moreover, p53 activates miRNA miR-200 to suppress EMT related CSC properties, ultimately leading to reduced tumor aggressiveness whereas natural agents target CSCs and reduce tumor aggressiveness by down-regulating miR-21 and up-regulating miR-200 and let-7.