have lower levels of activated oncogenes such as RAS and HMGA2. Therefore, expression levels of let-7 could be prognostic markers in several cancers associated with differentiation stages. In lung cancer, for example, reduced expression of let-7 is significantly correlated with reduced postoperative survival. The expression of let-7b and let-7g microRNAs are significantly associated with overall survival in 1262 breast cancer patients. Therapy Let-7 is also a very attractive potential therapeutic that can prevent tumorigenesis and angiogenesis, typically in cancers that underexpress let-7. Lung cancer, for instance, has several key oncogenic mutations including p53, RAS and MYC, some of which may directly correlate with the reduced expression of let-7, and may be repressed by introduction of let-7. Intranasal administration of let-7 has already been found effective in reducing tumor growth in a transgenic mouse model of lung cancer. Similar restoration of let-7 was also shown to inhibit cell proliferation in breast, colon and hepatic cancers, lymphoma, and uterine leiomyoma. References Further reading External links miRBase family entry for let-7 MicroRNA