In contrast, down regulated microRNAs, such as miR-125a and b and miR-205, regulate oncogenes as tyrosine kinase receptors HER2 and HER3, respectively [39,40], whereas let-7 has been described as a new regulator of self-renewal and tumorigenicity of breast cancer cells [41], targeting molecules originally described in lung cancer: RAS, HMGA2 and MYC. This evidence concerns the gene HMGA2 and breast carcinoma.