Dear Editor,rnIt is known that microRNA let-7a can be useful for diagnosis and therapy of cancer,including prostate cancer (PCa).1 A recent article by Wang et al.2 comprehensively showed that let-7a1 could inhibit the expression of insulin-like growth factor-1 receptor (IGF 1R) by directly targeting the T1 and T2 sites in the 3\' untranslated region (3\'UTR) of IGF 1R mRNA.Furthermore,they found that let-7a 1-mediated IGF 1R downregulation was accompanied by attenuation of Elk1 activity and c-fos expression,inhibition of PC-3 cell proliferation,cell cycle arrest and induced apoptosis and that inhibition of let-7al could up-regulate IGF 1R accompanied by an increase of Elk1 activity and c-fos expression,thereby enhancing cell proliferation.2 Their study is interesting and provides valuable data on the role of let-7a in PCa.Another study has3,in fact,demonstrated that let-7a directly bound to the 3\'UTR of E2F2 (E2F family of transcription factor) and CCND2 (cyclin D2) and downregulated their expression,leading to cell-cycle arrest at the G1/S phase and inhibit the PC-3 cells and LNCaP cells growth,especially in hormone-refractory PCa.In addition,xenograft models of PC-3 cells confirmed the capability of let-7a to inhibit prostate tumor development in vivo.