Vitamin D and microRNAs: Role in the pathogenesis and prognosis of breast cancer (Review)

A growing body of evidence has demonstrated how the development of breast cancer (BC) is associated with several environmental risk factors able to induce both genetic and epigenetic modifications, leading to neoplastic transformation. In this context, it has been shown how dietary factors influence BC cell development and progression by modulating epigenetic biomarkers, of which microRNAs (miRNAs/miRs) are one of the most extensively studied. Of note, dietary factors have been implicated in both BC risk and protection; a number of studies have focused on the protective role of vitamin D (VitD) in BC, as well as its potential therapeutic application in patients undergoing cancer treatments. Despite the numerous studies available in the literature, conflicting data are reported about the epigenetic modifications induced by VitD on the expression levels of miRNAs involved in BC. Therefore, the present review reports the latest findings describing the existing interplay between VitD and miRNAs and discusses the role of epigenetics in the pathogenesis and prognosis of this tumor. Specifically, the dual association existing between VitD and miRNAs in BC is described, presenting studies demonstrating the role of VitD and VitD receptor (VDR) in the modulation of the expression levels of several miRNAs, as well as the role of some miRNAs able to directly bind the mRNA coding for the VDR, thus regulating the activation of the VitD pathway.