Abstract
Over the past decade, non-coding RNAs (ncRNAs) have become a new paradigm of gene regulation. ncRNAs are classified into two major groups based on their size: long non-coding RNAs (lncRNAs) and small non-coding RNAs (including microRNAs, piRNAs, snoRNAs, and endogenous siRNAs). Here we review the recently emerging role of ncRNAs in mammary development, tumorigenesis, and metastasis, with the focus being on microRNAs (miRNAs) and lncRNAs. These findings shed new light on normal development and malignant progression, and suggest the potential for using ncRNAs as new biomarkers of breast cancer and targets for treatment.