Breast cancer (BC) is a multifactorial disease that is characterized by various genetic and epigenetic changes that occur due to the effect of various factors including that of environmental etiological agents. The obtained scientific data speak volumes for epigenetic dysregulation in BC pathogenesis. Out of all epigenetic markers, various microRNA regulating a wide spectrum of biological processes in a cell could be viewed as one of the predictors of potential risk. Understanding the functional role of these molecules will provide valuable information about the complex molecular mechanisms underlying the appearance and development of BC. This review summarizes currently existing publicly available data on aberrant expression of miR-125b, miR-181a, and miR-16 in case of various cancer localizations; analyzes their role in BC pathogenesis; presents an annotation of the target-genes; and evaluates the repression potential of microRNA and their diagnostic significance in case of BC. An analysis of changes in miRNA expression during radiation exposure was conducted. Interest in examining specific miRNAs is due to the results of long-term monitoring of the health of people living in radioactively contaminated areas of the Southern Urals, as well as data on the expression profiles of miR-125b, miR-181a, and miR-16 over the long term in exposed people.