Noncoding RNAs, Vital Players in Breast Cancer Metastasis

Breast cancer (BC) is the most common cause of deaths. Although recent medical advancements have improved survival of BC patients, the occurrence of metastasis increases mortality rate. Noncoding RNAs (ncRNAs) play important roles in BC metastasis (BCM). However, a detailed summary of ncRNAs involved in BCM is unavailable. Therefore, this review summarizes the key biological steps involved in BCM. We discussed the ncRNAs related to BCM according to "seed and soil" theory from four perspectives: (i) ncRNAs that make "breast cancer seed" preferable for BCM; (ii) ncRNAs that make "breast cancer seed" difficult for BCM; (iii) ncRNAs that make "breast cancer soil" preferable for BCM; (iv) ncRNAs that make "breast cancer soil" difficult for BCM. Lastly, we listed the ncRNAs and coding genes involved in BCM that act as initiators or suppressors. This review comprehensively overviews the biological mechanisms underlying BCM. The compiled evidence highlights the role of BCM-associated ncRNAs, which may serve as promising therapeutic targets for BCM.