Abstract: Breast cancer is the most common malignant tumor in women all over the world. It is a heterogeneous disease, and the exact cause of which is still unclear. However, breast cancer is composed of different subtypes with great differences in clinical characteristics, genetic background, and molecular markers. MicroRNAs (miRNAs) are small non-coding RNAs that regulate genes involved in various stages of key cellular processes after transcription. Persistent dysregulation of miRNAs plays a critical role in the malignant transformation of breast cancer cells, acting as carcinogens or tumor suppressors depending on their cellular environment. As a promising biomarker, dysregulation of miRNA expression seems to open up new opportunities for the diagnosis and prognosis of various cancers. Many studies have revealed the exact functions of miRNAs in different cancer types, however, the results have been inconsistent and further research is needed to determine the underlying mechanisms. In this review, miRNA is associated with the genetic and molecular background of breast cancer, the dual role of miRNA in breast can is described and summarized.

Key words: breast cancer, miRNA, dual role