In humans, let-7 is overexpressed in differentiated epithelial tissues and is oftentimes downregulated during tumorogenesis; it is known to target LIN28 mRNA and is itself a target of negative feedback regulation by LIN28.44, 52 LIN28 protein expression is upregulated in many tumors, including breast cancer.54 Let-7 was found to regulate breast cancer tumor-initiating cells (T-IC) through targeting HRAS and HMGA2.55 The miR-200 family is recognized as having a tumor-suppressor role. This evidence concerns the gene HRAS and breast cancer.