MicroRNAs in Breast Cancer; Growing Understanding of their Role in Metastasis and Invasion
Authors: AlHennawi Hussam , Bux Ahmed , Khan Tazim , Yousuf Fouad , Rayes Abdullah , Kazmi Suzanna , Anwer Lucman A. , Nurhussen Akram , Shareef Mohammad Abrar , Yaqinuddin Ahmed 
Published: November 2023

BackgroundMuch research has been done into finding specific molecular pathways involved in the metastatic and invasive potential of breast cancer cells. One of the major discoveries of this past decade has been microRNAs; which are single‐stranded non‐coding RNA molecules. Interestingly a single microRNA can influence the expression of hundreds of proteins, thereby highlighting their significance as modulators of gene expression. Apart from their role in regulating various intracellular processes, abnormal changes in microRNA expression have been linked to various human cancers. Until recently the nature and impact of most of these changes in breast cancer were unclear. However, some of the microRNA dysregulations have now been correlated with clinic‐pathological features such as Her2, ER and PR status, tumor stage, angiogenesis, metastasis and invasion. Of note to our study, compiling data has shown that microRNAs regulate cancer metastasis by influencing multiple steps in the metastatic cascade. This review will focus on key microRNAs associated with breast cancer invasion and metastasis; recently referred to as ‘metastamirs’.MethodsWe used the program EndNote X7 to research PubMed published articles regarding microRNAs in Breast Cancer. The terms “miRNAs” and “Breast cancer” were used as search words and the publication years were specified to range from 2005 to 2016. Our preliminary search revealed no articles pertaining to our topic before the year 2005, hence our paper covers nearly the entire literature on the topic. The retrieved records were then reviewed, and all those pertaining to metastasis and invasion in breast cancer were included in our study.ResultsOur EndNote search retrieved a total of 2820 abstracts, of which more than 280 were pertaining to metastasis and invasion in breast cancer. These abstracts were then read thoroughly, and roughly 130 metastasis/invasion specific microRNAs or clusters of microRNAs were identified. Interestingly, some microRNAs were shown to promote metastasis and invasion when up‐regulated, while others did so when they were down‐regulated. Nonetheless, all the identified microRNAs brought about their effects through various molecular pathways, some at more critical stages in the metastasis cascade than others. Figure 1 presents some of the commonly identified pro‐metastatic & anti‐metastatic microRNAs.ConclusionThe last decade has been revelationary with regards to non‐coding RNAs, microRNAs, and their association with various cancers. Our comprehensive review highlights the various microRNAs involved in key pathways within the breast cancer metastatic pathway. Co‐relating these microRNAs to clinically targetable pathophysiological points could revolutionize our fight against breast cancer; by not only serving as diagnostic & prognostic markers, but also being potential therapeutic targets. Carefully designed translational studies seem to be the call of the hour, to finally give us the much‐needed edge over breast cancer.Support or Funding InformationThe authors report no source of funding or support.