Among their targets, there are several cancer genes, such as RAS, MYC, HMGA2 and STAT3,20,21 and a negative feed-back loop between let-7 members and β-catenin has been described.22 Therefore, the low levels observed for let-7b and let-7c could be important in the development of ameloblastic odontomas and secondary ameloblastic carcinomas in K5-IKKβ mice or, alternatively, could be secondary to β-catenin overactivity. This evidence concerns the gene MYC and cancer.