The microRNAs (miRNAs) are an abundant class of small noncoding RNA molecules that regulate gene expression post-transcriptionally by interacting with messenger RNAs (mRNAs) and inducing either translation suppression or mRNA degradation.Although initial studies demonstrated a critical role of miRNAs in the control of fundamental processes of development, most recent studies have focused on the role of miRNAs in cancer.It has been found that cancers have a distinct miRNA expression signature, with the expression levels of most miRNAs being strongly reduced in human cancer cells and tissues.These findings suggest that miRNAs could be new targets for cancer treatment.We are interested in identifying miRNAs as novel therapeutic agents for breast cancer.Our recent findings in monolayer cell culture, three D cell culture and nude mouse xenograft tumor model studies will be presented and discussed.