Breast cancer is a malignant disease with a high incidence worldwide in women-and to less extent in men-, thus remains a health burden. miRNA plays a key role in the development and prognosis of breast cancer; as a single miRNA has the ability to regulate multiple gene targets and adversely alter their expression. In this review, we attempt to systematically analyze the rapidly accumulating body of research regarding the role of miRNAs subtypes particularly as oncogenes and biomarkers in breast cancer, and their clinical implications. A total of 11 pertinent articles in the past 10 years were extracted from high-rank reviews, analyzed, and summarized. Amongst many (eight miRNA subtypes), three subtypes (miR21, 155, and 10b) were selected in order to evaluate the validity of their oncogenicity as well as their diagnostic value as biomarkers.